This article describes an error verified (so far,) on Symantec PGP Universal 3.2.0 Build (1672).
The error in question is "unknown mail transport error", given by postfix, and can be found for mails in the local queue.
One reason can be malformed entries within the Mail Routes field, ie - domain.com - [X.Z.Y.Q ] . This can be verified if it's the cause by logging in with SSH, and do a:
less /etc/postfix/transport (q for quit)
# Postfix transport table
# Written by pgpsysconf - do not edit - your changes will be lost!
#
domain.com smtp:[X.Z.Y.Q ]
The cause for this is that pgpsysconf that re-generates the transport.db each time something is changed, does not trim the strings correctly, allowing the space to be left inside. Correct entries should look like this:
domain.com smtp:[X.Z.Y.Q]
To solve any problems with this - re-check any mail defined mail-routes.