Hi,
dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=smtp.gmail.com <http://smtp.gmail.com> type=AAAA: Host not found, try again)
This is you issue. DNS resolution is not working properly when vpn is active.
I assume that vpn pushes a dns configuration, so your box asks probably a dns server on the other side of the vpn to resolve internal names there.
For some reason this dns is not able to resolve smtp.gmail.com. This has to be investigated and fixed.
I think you can do further tests with simple "ping smtp.gmail.com" instead of checking postfix.
A quick hack solution could be to put an entry for smtp.gmail.com in your /etc/hosts file. But be aware that this hack breaks the day when gmail moves their server to another ip address.
Groetjes Claus -- Claus R. Wickinghoff, Dipl.-Ing. using Linux since 1994 and still happy... :-)
