We have an issue with certain users who are not able to receive email from specific external email accounts.
For example john@abc.com (external) sends an email to user1@scalix.com and to user2@scalix.com. The mail message is delivered to user1, but not user2. In the mail log you can see the message come into the server, but the nrcpts=1 (even though user2@scalix.com exists and the email address is correct).
Apr 22 21:09:02 mail sendmail[10885]: l3MD91Bm010885: from=<john@abc.com>, size=14720, class=0, nrcpts=1, msgid=<!&!AA, proto=ESMTP, daemon=MTA, relay=localhost [127.0.0.1]
If john@abc.com emails only user2@scalix.com, the mail log shows nrcpts=0 and size=0
Apr 22 21:08:37 mail sendmail[10881]: l3MD8Yil010881: from=<john@abc.com>, size=0, class=0, nrcpts=0, proto=ESMTP, daemon=MTA, relay=localhost [127.0.0.1]
We have this problem for several users now.