First, check the configuration with the following:
/usr/lib/sendmail -d0.1 -bt < /dev/null
The output will be something like this:
Version 8.11.6+Sun
Compiled with: LDAPMAP MAP_REGEX LOG MATCHGECOS MIME7TO8 MIME8TO7
NAMED_BIND NDBM NETINET NETINET6 NETUNIX NEWDB NIS NISPLUS
QUEUE SCANF SMTP USERDB XDEBUG
============ SYSTEM IDENTITY (after readcf) ============
(short domain name) $w = host
(canonical domain name) $j = host.mydomain.com
(subdomain name) $m = mydomain.com
(node name) $k = host
========================================================
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
It may show warnings or errors with the configuration.
Second, please explain the alias you entered - is it as follows?
On system abc.com
user1:
user1@def.com
This should tell sendmail to forward any mail for
user1@abc.com to
user1@def.com. You then have to insure that
user1@def.com accepts mail from abc.com (look in your sendmail.cf and aliases files).
Third, check that mail isn't suppose to stay on abc.com according to the sendmail.cf file on abc.com.