Outlook/Thunderbird Stalling

  • Outlook and Thunderbird are showing connected at both of our sites and are able to send/receive. After a few minutes of being connected, via vpn, to the Hmail server, the connection goes stale and does not receive email. The only way for it to "sync" up again is to close outlook and open it. I checked MTU values and they are all ok. I also tried the MSS Clamping option in pfsense with no luck. Has anyone else seen this issue or have any idea of what I could do to resolve it?


  • That definitely sounds like the usual scenario where you need MSS clamping enabled under System>Advanced, Misc, "Enable MSS clamping on VPN traffic". Note that only applies to new connections, so kill off the states, or completely reboot the client machines to ensure they aren't using already-established connections.

  • Thanks for the response. I will report back if that resolves the issue. I didn't think to clear the states and that may be why I'm still seeing the issues.


  • System -> Advanced Misc. Turn on MSS to limit the VPN traffic to 1400 (leave blank for this value). Fixed my issue. W00h00 :O)

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