The free plan supports 100000 emails per month, webhooks and has a very nice NodeJS API with a good (sufficient) documentation (the documentation for the general APIs is also good and completes the NodeJS documentation).
Here it is said that the content of the transmissions (emails) should not go over 20MBs. If you are using templates, then that content represents the ID of the currently used template, the content of the attachments and of the inline content.
To run example.js first run npm install in its directory and
complete the values of the first 4 variables declared at the beginning of the
script.
Other relevant links:
- SparkPost is based on the Momentum platform used by Facebook, between others such as LinkedIn, Twitter, PayPal, Oracle and Pinterest. "25% of global email is send through our software."
- Here MailChimp recommends SparkPost.
- The web UI looks similar to Mandrill, the API is cleaner than SendGrid's API and the template substitutions (merge vars) are more powerful than SendGrid's.
- The sending domains must be verified using the DNS records, which is different from SendGrid where domain verification is optional. With the sandbox domain you can only send 50 emails.
- It does not have a visual drag & drop HTML template designer like SendGrid although it has an HTML editor.