Using sendmail relay (SMART_HOST) through a spam filter
 

Good Morning,

I've kind of had support for linux email issues dropped in my lap and this is not really my strong suit.

Here's the situation and I hope I explain it right:

Red Hat Linux server used to generate emails. The client does not use their ISP for mail hosting and their linux server is not public, so their outgoing emails are relayed through the ISP mailserver via SMART_HOST in /etc/mail/sendmail.mc

define(`SMART_HOST',`mail.ispdomain.com')

Everything was working great until the ISP installed a spam filter on their mail server.

The out going email generated this error:

----- The following addresses had permanent fatal errors -----laura@recipient.com

----- Transcript of session follows -----
550 5.1.2 laura@recipient.com... Host unknown (Name server: mailsecurity.isp.com.ispdomain.com.: host not found)

--lA1Jcu017038.1193945936/linuxserver.com
Content-Type: message/delivery-status

Reporting-MTA: dns; ideal.com
Arrival-Date: Thu, 1 Nov 2007 15:38:11 -0400

Final-Recipient: RFC822; laura@recipient.com
Action: failed
Status: 5.1.2
Remote-MTA: DNS; mailsecurity.isp.com.ispdomain.com
Last-Attempt-Date: Thu, 1 Nov 2007 15:38:56 -0400

--lA1Jcu017038.1193945936/linuxserver.com
Content-Type: message/rfc822

The ISP provided me with a name and an IP address for the spamfilter.

Adding it to the DNS /etc/resolv.conf didn't help.

Replacing the SMART_HOST entry with it define(`SMART_HOST',`mailsecurity.isp.com')

regenerating sendmail.cf and restarting the sendmail service didn't help either, but I do get a new message:

----- The following addresses had permanent fatal errors -----
laura@recipient.com
(reason: 550 <laura@recipient.com>: Recipient address rejected: No such domain at this location (laura@recipient.com))

----- Transcript of session follows -----
... while talking to mailsecurity.isp.com.:
>>> RCPT To:<laura@recipient.com>
<<< 550 <laura@recipient.com>: Recipient address rejected: No such domain at this location (laura@recipient.com)
550 5.1.1 laura@recipient.com... User unknown

--lA1KT3119344.1193948943/linuxserver.com
Content-Type: message/delivery-status

Thanks for any help you can give me!

Laura

Question
 

Does the SPAM filter require that your sendmail log into the ISP's mail server as an authorized client? We had to restrict access to port 25 within our firewall. That means all our Linux servers had to log into our mail server as an authorized client.