RE: Sendmail behind firewall
The original problem was HELO check being compiled into the debian release
of sendmail caused harmless authentication -warning- messages. I noticed
these after moving my server behind the firewall and used a private IP. My
server complained when mail was relayed through anyone else stating the IP
was different than the MX record.
I assumed other host were doing the same check with me when a friend at
Ameritech.net couldn't mail to me. He assured me the messages were going to
his company account and he would try mailing from there. I thought my
private server IP not matching public MX record was the problem. I switched
back to public IP and everything was fine. His "test" messages came
through.
Then another message from same_friend@ameritech.net failed to deliver. He
said he was trying to send an attachment ... Surprised at this, I asked him
to send without attachment. No problem. He tried to mail attachment to his
yahoo account and then his work account. Nothing. Ameritech.net won't
deliver mail that has an attachment as an EXE. It must be zipped first!
Moved everything back to private IPs and it worked fine. I also contacted
sendmail who confirmed it should work fine. To deny delivery based on the
IP check would defeat NAT (or masquerade) firewall implementations.
Per Sendmail's Neil Wickert, it would violate the RFCs to deny the delivery
based on this IP verification. Issue resolved and sendmail humming!
Paul McHale
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