When you do thisover ADSL is there some MTU Overhead for the VPN also.

It is failing even though we can ping end points.

I.e Outlook fails even though telner <server> 25 works so seems to be some
packet size issue over the VPN.

Had the same problem for regular traffic without a VPN but adjusted various
MTU / PMTU sizes and all seemed OK.

Is there an equivalent for VPN MTU ?

G