If you read the posts people were telling you that the best way to solve this issue is to simply have the mail clients setup the Zimbra server as their smtp server and use SSL/TLS for the connection.
If you still insist on having clients connect through a VPN and then using port 25 for some bizarre reason, your best solution would be to find some sort of VPN server that supports accounts in LDAP and having it access the Zimbra server that way. This is a very complicated method for something that has been solved in a much better manner using mail clients... |