To check TLS

Command to get information about TLS communication for a recipient system

$openssl s_client  -starttls smtp -crlf -connect alt1.gmail-smtp-in.l.google.com:25

Sample Session details:

SMTP reply codes based on the SMTP commands

SMTP reply codes based on the SMTP commands


The following list groups the SMTP reply codes by the SMTP commands with which they can be associated. This can help you identify at what point the process failed.

HELO

250, 421, 500, 501, 504, 521

EHLO

250, 421, 500, 501, 504, 521

MAIL

250, 421, 451, 452, 500, 501, 552

RCPT

250, 251, 421, 450, 451, 452, 500, 501, 503, 521, 550, 551, 552, 553

DATA

354, 421, 451, 500, 501, 503, 554

SEND

250, 421, 451, 452, 500, 501, 502, 552

SOML

250, 421, 451, 452, 500, 501, 502, 552

SAML

250, 421, 451, 452, 500, 501, 502, 552

RSET

200, 250, 421, 500, 501, 504

VRFY

250, 251, 421, 500, 501, 502, 504, 550, 551, 553

EXPN

250, 421, 500, 501, 502, 504, 550

HELP

211, 214, 421, 500, 501, 502, 504

NOOP

200, 250, 421, 500

QUIT

221, 500

TURN

250, 500, 502, 503

SMTP Error Code

Question: How can I tell why an inbound or outbound message bounced, based on the SMTP reply code?

Solution:

If your inbound messages are bouncing back to the senders, have them inspect the bounced messages for SMTP reply codes generated by the message security service (see below). If the bounced messages contain codes generated by the message security service, then the message security service is at fault, and you can use those codes as a starting point for troubleshooting the cause of the messages not getting through.

If your outbound messages are bouncing, inspect them for the same system-generated codes, and apply the same troubleshooting principles.

In cases where the problem lies with your message security service, consult the Message Security Administration Guide.

If the bounced messages contain SMTP reply codes that were not generated by the message security service, then there is likely a problem with the sender’s or recipient’s mail server, or with the way the message was addressed. SMTP reply codes outside the scope of the message security service are also designed to aid in troubleshooting message delivery problems.