I am sending emails from an external domain to my domain zimbra. When I send emails without attaching files, the emails arrive on time ok. When I send mails with attachments, I get e-3 or 4 hours later.

My /var/log/zimbra.log I see nothing different than normal.

Sending mail attached to another external domain the mail arrives on time ok.

Are there any other file that I can review?

Thanks