My mail server has been experiencing strange problem. Emails sent from gmail and yahoo via blackberries failed to reach its intended recipients. Gmail and Yahoo mailer daemons would complain about connection timeout, and and then give up. My Trend Micro IMS antispam server log showed that google server initiated a session, but nothing happened after that. Whitelisting and increasing session timeout didn’t help.
I did notice unusual behaviour when telneting other SMTP servers from my mail server:
surfer@Mach5-M:~$ telnet smtp.cbn.net.id 25 Trying 18.104.22.168... Connected to smtp.cbn.net.id. Escape character is '^]'. 220 ********************* ehlo there 500 #5.5.1 command not recognized
This is due to our mail server sitting behind a Cisco ASA, and our network guy activating “inspect” on smtp traffics. After disabling “inspect” on the ASA with
# no inspect esmtp
email sent from gmail and yahoo via blackberries run normally and can be delivered to its target.