I’ve been getting the following error while trying to setup a SMTP submission service on port 587:
$ openssl s_client -connect SMTP.SERVER.COM:587
CONNECTED(00000003)
22564:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:s23_clnt.c:601:
It turns out this indicates that the smtp server ( qmail ) WAS setup properly on port 587. It’s just not an encrypted SMTP connection. Testing the same server via unencrypted Telnet session confirms this:
$ telnet smtp.jamboconsulting.com 587
Trying XX.XX.XX.XX…
Connected to SMTP.SERVER.COM.
Escape character is ‘^]’.
220 SMTP.SERVER.COM ESMTP
ehlo
250-SMTP.SERVER.COM
250-STARTTLS
250-PIPELINING
250 8BITMIME
exit
502 unimplemented (#5.5.1)
