I've Zimbra 6.0.7.
One user need al external pop account.

I've configured it on preferences and almost all work.

Problem is From field.

User account for external pop is user+domain.it
so in From I set "First Last name" and "user@domain.it".
On drop-down menu there are only zimbra email so I add correct email by hand.

Sending messare from this account "From:" field appear as username (user+domain.it) and not according with "From" field specification.