Solved: Email client stopped sending mail - Oct 2019
My email client stopped sending mail to smtp.comcast.net a few days ago. I read through some posts on this forum and noticed that some people were having success with setting their outgoing mail settings to "auto" security. So I set about discovering exactly what changed on the Comcast servers.
In a nutshell, Comcast is now requiring TLS when connecting to smtp.comcast.net
How you meet that requirement depends on your mail client (the application that you use to send mail). The settings that control security are usually in the same place were you specify the outgoing mail server (smtp options or sending mail). Be sure to use port 587 with smtp.comcast.net.
Read on for the gory details of my particular setup.
My Client Config
I run Postfix server on a Linux device and it is configured to relay all outgoing mail through smtp.comcast.net. I had previously configured it to use SSL on port 587 which worked for years.
Once Comcast starting requiring TLS my setup stopped working.
As it turns out, TLS is not on by default in my version of Postfix. As noted in the link, the smtp_tls_security_level option should be used with newer versions of Postfix. Set it to 'encrypt' to use TLS with Comcast servers.
Here's my updated SSL/TLS configuration (main.cf):
# SASL Authentication to the relay host:
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt
smtp_sasl_tls_security_options = noanonymous
Hope this helps!