Issue with Email-OAuth2-Proxy and TextOnly IMAP Configuration

[4S7xfPcbp1Hfayz]

Hello,

We are using email-oauth2-proxy as part of our migration to Exchange Online, since we have applications that do not support OAuth 2.0 authentication for email clients. Everything works perfectly except for one issue. Our application reads a mailbox, retrieves unread emails, processes them, and marks them as read. However, this is only partially working.

The emails are not being imported into our application but are being read and marked as read. Before migrating the mailbox to Exchange Online, we configured the following on our old setup(Exchange On Premise):

Set-CASMailbox -Identity xxxxx@xxxxx.com -ImapUseProtocolDefaults $false -ImapMessagesRetrievalMimeFormat TextOnly

I replicated this configuration in Exchange Online, but unfortunately, it is not working as expected. In the email-oauth2-proxy debug logs, I can see HTML content in the email bodies, whereas I should be seeing the TextOnly format.

Does the email-oauth2-proxy support the TextOnly MIME format for IMAP? If not, are there any workarounds to achieve this behavior?

Thank you for your help!

[simonrob]

This isn't something that is under the proxy's control – it handles the authentication step, but everything else in the connection proceeds as normal after that.

I suspect that either this setting isn't supported for Exchange Online, or there's a change in how it is applied. Alternatively, you could just change your application to select the text version of the message even if the HTML is present?