A user with an iPhone sends and email with an attachment to a recipient on a Zimbra server. The email is rejected and the following entry is made in the log:

Mar  8 16:08:41 mx2 postfix/cleanup[20141]: 654AD251CD: reject: header Content-Type: application/pdf;??name=FILENAME.pdf;??x-apple-part-url="5bf6655c-3ebc-e02d-b08a-0c1bd875c376@domainname.com" from mail.somemailserver.net[1.1.1.1]; from=<scott@domainname.com> to=<user@zimbraserver.com> proto=ESMTP helo=<mail.somemailserver.net>: 5.7.1 Attachment type not allowed. File "FILENAME.pdf;??x-apple-part-url="5bf6655c-3ebc-e02d-b08a-0c1bd875c376@domainanme.com" has the unacceptable extension "com"

Some iPhones add the domain name to the end of a x-apple-part-url header, and when the domain name ends in “.com” postfix is deciding the actual file name ends in “.com” and is rejecting it for that reason.

To avoid this problem, add the following two lines to the top of /opt/zimbra/conf/postfix_header_checks.in

%%uncomment VAR:zimbraMtaBlockedExtension%%/x-apple-part-url=\"?(.*)\.com\"?$/
%%uncomment VAR:zimbraMtaBlockedExtension%%     IGNORE

Then execute

su zimbra
postfix reload

Tested on Zimbra 8.6 and 8.7.2