Postfix is Wietse Venema's excellent mail server.
This container attempts to simplify and streamline setting up inbound and outbound mail relays, to protect and enhance self hosted email servers (eg: Microsoft Exchange). However, if you find an alternate use, please let me know so I can add to "Deployment Recipes".
The container employs Postfix's Postscreen for enhanced protection.
Apart from basic email relaying, the container can optionally:
- Implement up-to-date TLS/SSL security for SMTP connections
- Perform email virus scanning with ClamAV for all inbound/outbound email
- Implement DNSBLs for inbound email
- Perform DKIM signing for all outbound email
- Perform DKIM verification for all inbound email
- Implement spf checking for inbound email
- Implement greylisting for inbound email
- Implement LDAP-based recipient verification for inbound email
The container is fully configured via environment variables - each service's configuration files built from environment variables on container start. It also supports some configuration files via volume mappings.
Currently supported docker architectures are linux/386
, linux/amd64
, linux/arm/v7
and linux/arm64
.
Please note - docker hub cuts off this readme as it is quite long. To view the full readme click here.
This container implement's the excellent s6-overlay for process supervision (and a bunch of other handy stuff).
Service Name | Description | When is it started |
---|---|---|
postfix |
Runs postfix | Always |
clamav-milter |
Part of ClamAV. Runs the clamav-milter for scanning emails for virii. |
If ENABLE_CLAMAV is set to true |
clamd |
Part of ClamAV. Runs clamd , the virus scanning engine for clamav-milter . |
If ENABLE_CLAMAV is set to true |
freshclam |
Part of ClamAV. Runs freshclam on the schedule defined by FRESHCLAM_CHECKS_PER_DAY to keep the ClamAV database updated. |
If ENABLE_CLAMAV is set to true |
opendkim |
Runs opendkim for DKIM signing/verification. |
If ENABLE_OPENDKIM is set to true |
postgrey |
Runs postgrey for greylisting. |
If ENABLE_POSTGREY is set to true |
postgrey_whitelist_update |
Runs daily. Fetches the latest system whitelist from https://postgrey.schweikert.ch/pub/postgrey_whitelist_clients, merges with any locally defined whitelist, and reloads postgrey . |
If ENABLE_POSTGREY is set to true |
syslogd |
Present for opendkim and postgrey logging. |
Always |
In this deployment recipe, two containers (mail_in
and mail_out
) are created.
mail_in
is designed to sit between the internet and a local legacy Exchange server. It handles inbound email, and provides the following:
- Uses
postscreen
to ensure the sending MTA is standards compliant - Uses DNSBLs as an initial anti-spam measure
- Provides up-to-date TLS for incoming clients
- Performs greylisting as another anti-spam measure
- Performs SPF & DKIM verification
- Performs various header/sender/recipient checks to make sure the message is valid
- Performs recipient verification via LDAP to internal Active Directory
- Scans the email for viruses with ClamAV
- Forwards the email to the legacy Exchange server
mail_out
is designed to sit between the local legacy Exchange server and the internet. It handles outbound email, and provides the following:
- Provides up-to-date TLS for talking to external MTAs
- Performs DKIM signing
- Scans the email for viruses with ClamAV
- Delivers the outgoing email
From a networking perspective:
- The site's internet router is configured to NAT incoming connections on TCP port 25 through to the docker host running
mail_in
on port TCP 2525. - The site's Exchange server is configured to send email (via "smart host") to the docker host (which is hard-coded to TCP port 25)
An example docker-compose.yml
file is follows:
version: '3.8'
volumes:
queue_out:
driver: local
queue_in:
driver: local
certs:
driver: local
dkim:
driver: local
clamav_in:
driver: local
clamav_out:
driver: local
postgrey_in:
driver: local
tables_in:
driver: local
aliases_in:
driver: local
asupdata_in:
driver: local
logs_in:
driver: local
logs_out:
driver: local
services:
mail_out:
image: mikenye/postfix
container_name: mail_out
restart: always
logging:
driver: "json-file"
options:
max-file: "10"
max-size: "10m"
ports:
- "25:25"
environment:
TZ: "Australia/Perth"
POSTMASTER_EMAIL: "postmaster@yourdomain.tld"
POSTFIX_INET_PROTOCOLS: "ipv4"
POSTFIX_MYORIGIN: "mail.yourdomain.tld"
POSTFIX_PROXY_INTERFACES: "your.external.IP.address"
POSTFIX_MYNETWORKS: "your.local.LAN.subnet/prefix"
POSTFIX_MYDOMAIN: "yourdomain.tld"
POSTFIX_MYHOSTNAME: "mail.yourdomain.tld"
POSTFIX_MAIL_NAME: "outbound"
POSTFIX_SMTPD_TLS_CHAIN_FILES: "/etc/postfix/certs/privkey.pem, /etc/postfix/certs/fullchain.pem"
POSTFIX_SMTP_TLS_CHAIN_FILES: "/etc/postfix/certs/privkey.pem, /etc/postfix/certs/fullchain.pem"
POSTFIX_SMTPD_TLS_SECURITY_LEVEL: "may"
POSTFIX_SMTPD_TLS_LOGLEVEL: 1
POSTFIX_REJECT_INVALID_HELO_HOSTNAME: "false"
POSTFIX_REJECT_NON_FQDN_HELO_HOSTNAME: "false"
POSTFIX_REJECT_UNKNOWN_HELO_HOSTNAME: "false"
ENABLE_OPENDKIM: "true"
OPENDKIM_SIGNINGTABLE: "/etc/mail/dkim/SigningTable"
OPENDKIM_KEYTABLE: "/etc/mail/dkim/KeyTable"
OPENDKIM_MODE: "s"
OPENDKIM_INTERNALHOSTS: "your.local.LAN.subnet/prefix"
OPENDKIM_LOGRESULTS: "true"
OPENDKIM_LOGWHY: "true"
ENABLE_CLAMAV: "true"
CLAMAV_MILTER_REPORT_HOSTNAME: "mail.yourdomain.tld"
volumes:
- "certs:/etc/postfix/certs:ro"
- "dkim:/etc/mail/dkim:rw"
- "clamav_out:/var/lib/clamav:rw"
- "queue_out:/var/spool/postfix:rw"
- "logs_out:/var/log:rw"
mail_in:
image: mikenye/postfix
container_name: mail_in
restart: always
logging:
driver: "json-file"
options:
max-file: "10"
max-size: "10m"
dns:
- 8.8.8.8
- 8.8.4.4
ports:
- "2525:25"
environment:
TZ: "Australia/Perth"
POSTMASTER_EMAIL: "postmaster@yourdomain.tld"
POSTFIX_INET_PROTOCOLS: "ipv4"
POSTFIX_MYORIGIN: "mail.yourdomain.tld"
POSTFIX_PROXY_INTERFACES: "your.external.IP.address"
POSTFIX_MYDOMAIN: "yourdomain.tld"
POSTFIX_MYHOSTNAME: "mail.yourdomain.tld"
POSTFIX_MAIL_NAME: "inbound"
POSTFIX_SMTPD_TLS_CHAIN_FILES: "/etc/postfix/certs/privkey.pem, /etc/postfix/certs/fullchain.pem"
POSTFIX_SMTP_TLS_CHAIN_FILES: "/etc/postfix/certs/privkey.pem, /etc/postfix/certs/fullchain.pem"
POSTFIX_SMTPD_TLS_SECURITY_LEVEL: "may"
POSTFIX_SMTPD_TLS_LOGLEVEL: 1
POSTFIX_RELAYHOST: "exchange.server.IP.addr"
POSTFIX_RELAY_DOMAINS: "yourdomain.tld,someotherdomain.tld"
POSTFIX_DNSBL_SITES: "hostkarma.junkemailfilter.com=127.0.0.2, bl.spamcop.net, cbl.abuseat.org=127.0.0.2, zen.spamhaus.org"
ENABLE_OPENDKIM: "true"
OPENDKIM_MODE: "v"
OPENDKIM_LOGRESULTS: "true"
OPENDKIM_LOGWHY: "true"
ENABLE_SPF: "true"
ENABLE_CLAMAV: "true"
CLAMAV_MILTER_REPORT_HOSTNAME: "mail.yourdomain.tld"
ENABLE_POSTGREY: "true"
ENABLE_LDAP_RECIPIENT_ACCESS: "true"
POSTFIX_LDAP_SERVERS: "active.directory.server.IP,active.directory.server.IP"
POSTFIX_LDAP_BIND_DN: "CN=mailrelay,OU=Service Accounts,OU=Users,DC=yourdomain,DC=tld"
POSTFIX_LDAP_BIND_PW: "12345"
POSTFIX_LDAP_SEARCH_BASE: "DC=yourdomain,DC=tld"
volumes:
- "certs:/etc/postfix/certs:ro"
- "queue_in:/var/spool/postfix:rw"
- "clamav_in:/var/lib/clamav:rw"
- "postgrey_in:/etc/postgrey:ro"
- "tables_in:/etc/postfix/tables:ro"
- "aliases_in:/etc/postfix/local_aliases:ro"
- "logs_in:/var/log:rw"
It is recommended to make your volume mounts somewhere you can access them, so you can edit files, load certificates, view logs easily, etc.
For example, you could map through to a known local path:
volumes:
queue_out:
driver: local
type: 'none'
o: 'bind'
device: '/opt/mail/queue_out'
...
...or, another example useing NFS to a filer/server, eg:
volumes:
queue_out:
driver: local
type: nfs
o: addr=1.2.3.4,rw
device: ":/vol/mail/queue_out"
...
Environment Variable | Description |
---|---|
ENABLE_CLAMAV |
Optional. Set to "true" to enable ClamAV. Default is "false". |
ENABLE_LDAP_RECIPIENT_ACCESS |
Optional. Enable LDAP-based recipient verification. See LDAP Recipient Verification section below. |
ENABLE_OPENDKIM |
Optional. Set to "true" to enable OpenDKIM. If OpenDKIM is enabled, the "OpenDKIM Configuration" variables below will need to be set. Default is "false". |
ENABLE_POSTGREY |
Optional. Set to "true" to enable postgrey. Default is "false". |
ENABLE_SPF |
Optional. Set to "true" to enable policyd-spf. Default is "false". |
POSTMASTER_EMAIL |
Required. Set to the email of your domain's postmaster. Example: postmaster@domain.tld . |
TZ |
Recommended. Set the timezone for the container. Default is UTC . |
Environment Variable | Description |
---|---|
SYSLOG_PRIORITY |
Optional. Log only messages more urgent than SYSLOG_PRIORITY . 0 = Emergency, 1 = Alert, 2 = Critical, 3 = Error, 4 = Warning, 5 = Notice, 6 = Info (the default), 7 = Debug |
Environment Variable | Documentation Link |
---|---|
POSTFIX_DNSBL_SITES |
See documentation link. |
POSTFIX_DNSBL_THRESHOLD |
See documentation link. |
POSTFIX_INET_PROTOCOLS |
See documentation link. |
POSTFIX_MAIL_NAME |
See documentation link. |
POSTFIX_MESSAGE_SIZE_LIMIT |
See documentation link. |
POSTFIX_MYDOMAIN |
See documentation link. |
POSTFIX_MYHOSTNAME |
See documentation link. |
POSTFIX_MYNETWORKS |
See documentation link. |
POSTFIX_MYORIGIN |
See documentation link. |
POSTFIX_PROXY_INTERFACES |
See documentation link. |
POSTFIX_REJECT_INVALID_HELO_HOSTNAME |
See documentation link. |
POSTFIX_REJECT_NON_FQDN_HELO_HOSTNAME |
See documentation link. |
POSTFIX_REJECT_UNKNOWN_HELO_HOSTNAME |
See documentation link. |
POSTFIX_RELAY_DOMAINS |
See documentation link. |
POSTFIX_RELAYHOST_PORT |
Optional port argument for POSTFIX_RELAYHOST . Default is 25 so only need to change if you're relayhost is running on a different port. |
POSTFIX_RELAYHOST |
See documentation link. |
POSTFIX_SMTP_TLS_CHAIN_FILES |
See documentation link. |
POSTFIX_SMTPD_MILTERS |
Any milters given here are applied after DKIM & ClamAV. See documentation link. |
POSTFIX_SMTPD_RECIPIENT_RESTRICTIONS_PERMIT_SASL_AUTHENTICATED |
Set to true to include in smtpd_recipient_restrictions . See documentation link. |
POSTFIX_SMTPD_TLS_CERT_FILE |
See documentation link. |
POSTFIX_SMTPD_TLS_CHAIN_FILES |
See documentation link. |
POSTFIX_SMTPD_TLS_KEY_FILE |
See documentation link. |
POSTFIX_SMTPD_TLS_LOGLEVEL |
See documentation link. |
POSTFIX_SMTPD_TLS_SECURITY_LEVEL |
See documentation link. |
POSTFIX_SMTPD_USE_TLS |
See documentation link. |
POSTFIX_SMTPUTF8_ENABLE |
See documentation link. |
POSTFIX_CHECK_RECIPIENT_ACCESS_FINAL_ACTION |
If recipient checks are enabled (via ENABLE_LDAP_RECIPIENT_ACCESS and/or recipient_access.hash ), this is the final action taken after all other checks. Default is defer . Usually should be set to either defer or reject . See documentation link. |
See "LDAP" section below.
If ENABLE_LDAP_RECIPIENT_ACCESS
is enabled, the final smtpd_recipient_restrictions
action becomes defer
(from the default of permit
).
Environment Variable | Documentation Link |
---|---|
POSTFIX_LDAP_SERVERS |
Required. Comma separated list of LDAP servers. |
POSTFIX_LDAP_VERSION |
Optional. LDAP version. Default is 3 (which works with Active Directory). |
POSTFIX_LDAP_QUERY_FILTER |
Optional. LDAP query filter to find user/group emails. Default is `(&( |
POSTFIX_LDAP_SEARCH_BASE |
Required. The base DN in which to search for users/groups. eg: DC=MyDomain,DC=tld . |
POSTFIX_LDAP_BIND_DN |
Required. The account name to use to bind to the LDAP servers, specified in LDAP syntax, eg: CN=svc-mailrelay,OU=Service Accounts,OU=Users,DC=MyDomain,DC=tld . |
POSTFIX_LDAP_BIND_PW |
Required. The account password for the POSTFIX_LDAP_BIND_DN account. |
POSTFIX_LDAP_DEBUG_LEVEL |
Optional. If you're having problems, you can set this to 1 or higher. |
Environment Variable | Detail |
---|---|
OPENDKIM_DOMAIN |
Comma separated list of domains whose mail should be signed by this filter. |
OPENDKIM_INTERNALHOSTS |
Comma separated list of internal hosts whose mail should be signed rather than verified. |
OPENDKIM_KEYFILE |
Gives the location (within the container) of a PEM-formatted private key to be used for signing all messages. |
OPENDKIM_KEYTABLE |
Path to a key table. You do not need to include refile: . Can be used instead of OPENDKIM_KEYFILE & OPENDKIM_SELECTOR for multiple domains. |
OPENDKIM_LOGRESULTS |
Set to true for for logging of the results of evaluation of all signatures that were at least partly intact. |
OPENDKIM_LOGWHY |
Set to true for very detailed logging about the logic behind the filter’s decision to either sign a message or verify it. |
OPENDKIM_MODE |
Selects operating modes. The string is a concatenation of characters that indicate which mode(s) of operation are desired. Valid modes are s (signer) and v (verifier). The default is sv except in test mode (see the opendkim(8) man page) in which case the default is v. When signing mode is enabled, one of the following combinations must also be set: (a) Domain, KeyFile, Selector, no KeyTable, no SigningTable; (b) KeyTable, SigningTable, no Domain, no KeyFile, no Selector; (c) KeyTable, SetupPolicyScript, no Domain, no KeyFile, no Selector. |
OPENDKIM_SELECTOR |
Set to the selector specified when creating the Key File. |
OPENDKIM_SIGNINGTABLE |
Path to a signing table file. You do not need to include refile: . Can be used instead of OPENDKIM_DOMAIN for multiple domains. |
OPENDKIM_SUBDOMAINS |
Set to true to sign subdomains of those listed by the Domain parameter as well as the actual domains. |
Environment Variable | Detail |
---|---|
FRESHCLAM_CHECKS_PER_DAY |
Optional. Number of database checks per day. Default: 12 (every two hours). |
CLAMAV_MILTER_REPORT_HOSTNAME |
Optional. The hostname ClamAV Milter will report in the X-Virus-Scanned header. If unset, defaults to the container's hostname. |
CLAMAV_CLAMD_PHISHING_SIGNATURES |
Optional. Overrides ClamAV Daemon's default setting for PhishingSignatures . |
CLAMAV_CLAMD_PHISHING_SCAN_URLS |
Optional. Overrides ClamAV Daemon's default setting for PhishingScanURLs . |
CLAMAV_CLAMD_PHISHING_ALWAYS_BLOCK_SSL_MISMATCH |
Optional. Overrides ClamAV Daemon's default setting for PhishingAlwaysBlockSSLMismatch . |
CLAMAV_CLAMD_PHISHING_ALWAYS_BLOCK_CLOAK |
Optional. Overrides ClamAV Daemon's default setting for PhishingAlwaysBlockCloak . |
CLAMAV_CLAMD_HEURISTIC_SCAN_PRECEDENCE |
Optional. Overrides ClamAV Daemon's default setting for HeuristicScanPrecedence . |
The following files can be optionally configured.
If using postfix table files, it is recommened to place all files into a single directory, and map this directory through to the container at /etc/postfix/tables
.
Table File (with respect to container) | Format | If this file is present... | After modifying... |
---|---|---|---|
/etc/postfix/tables/client_access.cidr |
cidr | It is automatically added to postfix's check_client_access . |
Run helper command update_client_access (see below) |
/etc/postfix/tables/dnsbl_reply.texthash |
texthash | It is automatically added to postfix's postscreen_dnsbl_reply_map . |
Run helper command update_dnsbl_reply (see below) |
/etc/postfix/tables/header_checks.pcre |
pcre | It is automatically added to postfix's header_checks . |
Run helper command update_header_checks (see below) |
/etc/postfix/tables/helo_access.hash |
hash | It is automatically added to postfix's check_helo_access . |
Run helper command update_helo_access (see below) |
/etc/postfix/tables/milter_header_checks.pcre |
pcre | It is automatically added to postfix's milter_header_checks . |
Run helper command update_milter_header_checks (see below) |
/etc/postfix/tables/postscreen_access.cidr |
cidr | It is automatically added to postfix's 'postscreen_access_list' (after permit_mynetworks ). |
Run helper command update_postscreen_access (see below) |
/etc/postfix/tables/sender_access.hash |
hash | It is automatically added to postfix's check_sender_access . |
Run helper command update_sender_access (see below) |
/etc/postfix/tables/recipient_access.hash |
hash | It is automatically added to postfix's check_recipient_access , and the final smtpd_recipient_restrictions action becomes defer (from the default of permit ). |
Run helper command check_recipient_access (see below) |
For the format of this file, see the postgrey manpage.
Configuration file (with respect to container) | If this file is present... | After modifying... |
---|---|---|
/etc/postgrey/postgrey_whitelist_clients.local |
It is merged with the regularly updated system whitelist. | Run helper command update_postgrey_whitelist (see below). |
The system whitelist is downloaded from https://postgrey.schweikert.ch/pub/postgrey_whitelist_clients once every 24 hours if postgrey is enabled.
The format of this file is as-per the /etc/aliases
file.
Configuration file (with respect to container) | If this file is present... | After modifying... |
---|---|---|
/etc/postfix/local_aliases/aliases |
It is merged with the system aliases file. | Run helper command update_aliases (see below). |
The system aliases file maps postmaster
, root
, postfix
and clamav
through to the address specified by POSTMASTER_EMAIL
.
Path | Access | Detail |
---|---|---|
/var/spool/postfix |
rw |
Required. Mail queue & postgrey database. |
Path | Access | Detail |
---|---|---|
/var/lib/clamav |
rw |
ClamAV anti-virus database. Map if using ClamAV. |
/etc/postfix/local_aliases |
rw |
A file named aliases can be placed in this folder. The contents of this file will be added to the container's /etc/aliases at startup. Map if you need to add entries to /etc/aliases . |
/etc/postfix/certs |
ro |
Postfix TLS chain files should be placed in here. Map if using TLS/SSL. |
/etc/postgrey |
ro |
Postgrey local whitelists should be placed in here. Map if using postgrey. |
/etc/postfix/tables |
ro |
Postfix's tables should be placed in here. Map if you need to use any of the Postfix Table Files listed above. |
/etc/mail/dkim |
rw |
DKIM private keys (and KeyTable /SigningTable files if used) to be placed here. |
When setting up DKIM, you can use this container to create your keys.
Change to a directory on the host that will hold the public & private keys.
cd /path/to/dkim/keys
Generate a key with the following command (replacing your.domain.name
with your domain name):
docker run \
--rm \
-it \
-v $(pwd):/workdir \
--entrypoint opendkim-genkey \
mikenye/postfix \
--directory=/workdir \
--bits=1024 \
--selector=<selector> \
--restrict \
--domain=<yourdomain.tld>
There should now be two files in your current directory, <selector>.private
and <selector>.txt
. This directory should be mapped through to the container (I suggest at /etc/mail/dkim
), and the full path of the <selector>.private
file (with respect to the container's filesystem) should be passed to OPENDKIM_KEYFILE
. The <selector>
should be passed to OPENDKIM_SELECTOR
.
If you have more than one domain to sign mail for, you can use KeyTable
and SigningTable
files.
The <selector>.txt
files contain DNS records which should be added to yourdomain.tld
's DNS.
As for a selector name, an example may be: “sales-201309-1024”. This example indicates that it belongs to the “sales” email stream, is intended to be rotated into active duty in September 2013 and references a 1024-bit key (reference).
For more information, see the OpenDKIM readme: http://opendkim.org/opendkim-README
With LDAP-based recipient verification:
- Before accepting email, when postfix receives an
RCPT TO
, it will query LDAP for the address given. - If LDAP finds an email address in your directory, the message will be accepted.
- If LDAP does not find an email address in your directory, the message will be deferred (status code 450).
This is usually a good idea, because it saves resources on your internal mail server. For example, a client runs MS Exchange & Kaspersky Security for Mail Server. Kaspersky scans all mail that hits the Exchange server, regardless of whether or not there is a valid recipient for the email. This means that if mail is sent to a non-existent address, you have the overhead of:
- The postfix container processing & scanning the email
- Kaspersky scanning the email
- Exchange processing the email, generating a bounce message
- Exchange & postfix trying to deliver the bounce message
With recipient verification, the sender is given a deferral, and after some time they will get a bounce message.
If setting this up for the first time:
- It is suggested to check the container log (grep for
" 450 "
) occasionaly to make sure there are no accidental deferrals. - If there are accidental referrals, or you have addresses that email should be accepted for that are not in your directory, you can add these to the
recipient_access.hash
file (see above). The next time the message delivery is attempted (because we are deferring, not rejecting), it should deliver properly.
See the Postfix LDAP Howto for more information.
These commands can be executed in the context of the container, for example:
docker exec <container> <command>
Command | Purpose |
---|---|
postfix reload |
Performs a postfix reload (should be done if SSL certs are updated, etc). |
If you edit one of postfix's table files, you must run the appropriate helper command below before the new version of the table file will be active.
Command | Purpose |
---|---|
update_aliases |
Rebuilds /etc/aliases within the container, and runs newaliases . |
update_client_access |
Rebuilds files used by check_client_access . |
update_dnsbl_reply |
Rebuilds files used by postscreen_dnsbl_reply_map . |
update_header_checks |
Rebuilds files used by header_checks . |
update_helo_access |
Rebuilds files used by check_helo_access . |
update_milter_header_checks |
Rebuilds files used by milter_header_checks . |
update_postgrey_whitelist |
Rebuilds files used by postgrey's --whitelist-clients . |
update_postscreen_access |
Rebuilds files used by postscreen_access_list . |
update_recipient_access |
Rebuilds files used by check_recipient_access . |
update_sender_access |
Rebuilds files used by check_sender_access . |
postscreen_access_list
:permit_mynetworks
- includes any networks set by thePOSTFIX_MYNETWORKS
environment variablecidr:/etc/postfix/postscreen_access.cidr
- includes any local entries added to/etc/postfix/tables/postscreen_access.cidr
. If you are using fail2ban or similar, this is the file you can add your banned IPs to.- If
POSTFIX_DNSBL_SITES
is configured, postscreen performs DNSBL checks.
smtpd_helo_restrictions
:permit_mynetworks
- includes any networks set by thePOSTFIX_MYNETWORKS
environment variablecheck_helo_access hash:/etc/postfix/helo_access.hash
- includes any local entries added to/etc/postfix/tables/helo_access.hash
reject_invalid_helo_hostname
- unless the environment variablePOSTFIX_REJECT_INVALID_HELO_HOSTNAME
is set tofalse
reject_non_fqdn_helo_hostname
- unless the environment variablePOSTFIX_REJECT_NON_FQDN_HELO_HOSTNAME
is set tofalse
reject_unknown_helo_hostname
- unless the environment variablePOSTFIX_REJECT_UNKNOWN_HELO_HOSTNAME
is set tofalse
smtpd_recipient_restrictions
:permit_mynetworks
- includes any networks set by thePOSTFIX_MYNETWORKS
environment variablecheck_client_access cidr:/etc/postfix/client_access.cidr
- includes any local entries added to/etc/postfix/tables/client_access.cidr
permit_sasl_authenticated
- see: http://www.postfix.org/postconf.5.html#permit_sasl_authenticated. This is placed belowcheck_client_access
so that malicious actors can be blocked viaclient_access.cidr
check_sender_access hash:/etc/postfix/sender_access.hash
- includes any local entries added to/etc/postfix/tables/header_checks.pcre
reject_unauth_destination
- see: http://www.postfix.org/postconf.5.html#reject_unauth_destination. This is placed above more "expensive" checks to prevent wasting resources for mail that's going to be rejected.- If
ENABLE_SPF
is enabled,check_policy_service unix:private/policy
- performs SPF checks. reject_non_fqdn_recipient
- see: http://www.postfix.org/postconf.5.html#reject_non_fqdn_recipient.reject_non_fqdn_sender
- see: http://www.postfix.org/postconf.5.html#reject_non_fqdn_sender.reject_unknown_sender_domain
- see: http://www.postfix.org/postconf.5.html#reject_unknown_sender_domain.reject_unknown_recipient_domain
- see: http://www.postfix.org/postconf.5.html#reject_unknown_recipient_domain.- If
ENABLE_POSTGREY
is enabled,check_policy_service inet:127.0.0.1:10023
- performs greylisting. - If
ENABLE_LDAP_RECIPIENT_ACCESS
is enabled, and/or if/etc/postfix/tables/recipient_access.hash
exists,check_recipient_access ...
- performs recipient address verification using LDAP and/or therecipient_access.hash
file. Therecipient_access.hash
file is analysed first, allowing this file to override LDAP verification. - Finally:
- If
check_recipient_access
is used (see above), then:POSTFIX_CHECK_RECIPIENT_ACCESS_FINAL_ACTION
(default:defer
) - Else:
permit
smtpd_data_restrictions
:reject_unauth_pipelining
- see: http://www.postfix.org/postconf.5.html#reject_unauth_pipeliningpermit
After a message is queued, it is passed through milters:
- If
ENABLE_DKIM
, the email is sent throughopendkim
. The email is signed/verified by DKIM. - If
ENABLE_CLAMAV
, the email is sent throughclamav-milter
. The email is dropped if a virus is detected. - If any additional milters are defined with
POSTFIX_SMTPD_MILTERS
, they are then applied.
To test your configuration, an expect
script is included in the GitHub Repo.
The script requires telnet
.
The syntax of the file is as follows:
test_server.expect <mail_server> <port> <helo> <from> <to>
Where:
<mail_server>
is the IP/hostname of the mail server<port>
is the port of the mail server<helo>
is the FQDN to identify as<from>
is the sender email<to>
is the recipient email
An email will be sent from <from>
, to <to>
with the subject Test email sent at <date/time>
.
expect
is used to wait for the server to respond properly between commands, to prevent the session from being terminated due to Postfix's reject_unauth_pipelining
.
When setting this container up, it is recommended to:
- For inbound mail relays, from an external server:
- Test normal operation - Test from an external email address, to an internal mail address.
- Test to ensure no open relay - Test from an internal email address, to an external mail address.
- For outbound mail relays, from an internal server (as your outbound mail relay should not be accessable outside your LAN):
- Test normal operation - Test from an internal email address, to an external mail address.
- For testing SPF/DKIM - there are online tools available, such as https://email-test.had.dnsops.gov (remember that this service is rate limited, so don't accidentally get banned by testing too much). Furthermore, you can send an email to a gmail address and then take a look at the headers when (if) the message arrives. Google performs SPF/DKIM/DMARC on all email.
Please feel free to open an issue on the project's GitHub.
I also have a Discord channel, feel free to join and converse.
- http://www.postfix.org/documentation.html: Postfix Documentation.
- http://opendkim.org/opendkim-README: OpenDKIM Readme.
- https://www.skelleton.net/2015/03/21/how-to-eliminate-spam-and-protect-your-name-with-dmarc/: A fantastic HOWTO (dated, but still very much relevant).
- https://petervibert.com/wp/expect-smtp-script/: plagiarized their expect script and made some modifications for the testing script.