Disable Plain-Text SMTP and Enforce STARTTLS for Client Connections | Postal SMTP Server

[thomasr007]

Hi Team,

How can we restrict non-encrypted SMTP communication from clients? Our requirement is that clients should be able to communicate with the Postal server only using STARTTLS over port 587 or port 25. Plain-text (unencrypted) connections should not be allowed.

Could you please help us with the required configuration?

Originally posted by @thomasr007 in #3540 (comment)

[willpower232]

Unfortunately for your use case, Postal requires initial connections to be unencrypted and then optionally upgraded to encrypted with STARTTLS.

You might be able to update this file so that start_tls and tls were always true but I don't know how well that would work

https://github.com/postalserver/postal/blob/main/app/lib/smtp_server/client.rb

Alternatively, you could add in something to return error codes if tls was false so that clients must use STARTTLS to send anything.