Here's a few tricks to help debug sendmail problems: Finding the sendmail version:

sendmail -d0.1 -bt < /dev/null

Checking for valid MX records:

sendmail -bt > /mx in2nix.com

Should get back a list of MX records OR

nslookup -q=mx in2nix.com

You can check a target destination with:

sendmail -bt > /map host in2nix.com

Error messages are usually logged in the messages/syslog file, e.g. /var/adm/ messages on Solaris. However, this is dependent on the configuration of syslog

A common sendmail error is unknown host mailhost 550 . This can be caused by sendmail not recognising the DNS domain. e.g. if the host is improperly defined in /etc/hosts:

192.168.2.1 host1 host1.

instead of

192.168.2.1 host1 host1.in2nix.com

To check what sendmail thinks the domain is run:

sendmail -d0.1 -bt < /dev/null

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