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Troubleshooting SMTP

Troubleshooting SMTP

This page is primarily for the team. It's public so that you can learn from it. For help using, see the user docs.


Often times a service is functioning properly, but mail will not deliver. The general root cause for this is the mail service silently rejecting mail, or sometimes a firewall change.

Mail Relay

All outgoing mail should be sent via the internal mail relay listed in Terraform outputs.


SMTP Authentication should be used to send mail. In order to communicate, the username and password need to be sent base64 encoded:

# Get the username in base64
echo -n "username" | base64

# Get the password in base64
echo -n "password" | base64

Sending a test email

“VXNlcm5hbWU6” is base64 for “Username:“. “UGFzc3dvcmQ6” is base64 for “Password:“.

# Connect to the server
openssl s_client -starttls smtp -connect RELAYIP:25
334 VXNlcm5hbWU6
334 UGFzc3dvcmQ6
235 2.7.0 Authentication successful
MAIL from: <>
250 2.1.0 Ok
RCPT to: <>
250 2.1.5 Ok
354 End data with <CR><LF>.<CR><LF>
Subject: Our mail really does work

We have worked with the best scientists abroad, and found that indeed this works.
250 2.0.0 Ok: queued as A0F8860435
221 2.0.0 Bye