By default, emails with an encrypted PDF or archive (i.e. zip) attachment will be blocked by Zimbra’s antivirus program, ClamAV. The user will be notified by an email titled ‘VIRUS (Heuristics.Encrypted.PDF) in mail FROM….’ with a message containing ‘A virus was found: Heuristics.Encrypted.PDF’. The original message itself will be quarantined and inaccessible to the user.

To allow encrypted files to pass through to the recipient, The Global AS/AV setting ‘Block Encrypted Files’ needs to be disabled.  It is possible to set it from the command line (as the zimbra user) with the command: zmprov mcf zimbraVirusBlockEncryptedArchive FALSE and then a restart of the server with: zmcontrol restart.