I have sendmail running on Red Hat, and have set up the program vacation to enable autoresponding to users. For some reason, vacation autoresponds only to local users. For instance, when vacation is set up for email@example.com, if firstname.lastname@example.org sends a message to user1, then user2 does get the configured autoresponse message. If email@example.com sends a message to firstname.lastname@example.org, he does not get an autoresponse.
Please note that the mailserver is sitting behind a firewall. The IP of domain.net is obviously that of the firewall which forwards connections to mail ports to the mail server.
Thank you for the help.