Delay sending mail to server

Hi everybody,

Users in my company are experience some problems when they replicate their mails from outside the office.

When they are out of the office, they use a VPN connection and replicate their mails from the Server to Local without any problem, but when it is time to send mails to server it is taking too much time, 1 or 2 hours or in many cases they operation can not be finished.

Have any of you knows if there is any setting I must check on my Domino Server o LN clients?

Thnks!