If mail does not go out of MS Outlook

So, if your users are complaining that theire mail is not leaving MS Outlook, and you are looking at your mail server and all looks well (Sendmail/MailScanner combo), here is what can be done to locate the problem :

From your mail server do these two commands, and time how long it takes in both cases :
# telnet 127.0.0.1 25
Trying 127.0.0.1…
Connected to 127.0.0.1.
Escape character is ‘^]’.
220 mail-2012.my.domain ESMTP Sendmail 8.14.4/8.14.4; Tue, 13 Aug 2013 11:28:29 +0200
…..

Server FQDN is mail-2012.my.domain, and its 10.10.10.36 is its internal IP address :
# telnet 10.10.10.36 25
Trying 10.10.10.36…
Connected to 10.10.10.36.
Escape character is ‘^]’.
220 mail-2012.my.domain ESMTP Sendmail 8.14.4/8.14.4; Tue, 13 Aug 2013 11:28:53 +0200
…..

If call per IP address takes MUCH longer than the one per lo (127.0.0.1), the problem may be in /etc/hosts file.
In RHEL6U4 (for some totally mysterious reason) after restart, all manual inputs to files /etc/resolv.conf and /etc/hosts are whipped out.
Here is what SHOULD be in /etc/hosts file :
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
10.10.10.36 mail.my.domain
…..

It means that you HAVE to have a link between server local IP address and its FQDN. It it is not there, insert it, and things should start to get better.

Also think about making a small script to copy back to location those two files, after each restart.

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