Mail Connector fails to flow from O365 to Domino after a period of time (4348169)

• Coexistence Manager for Notes (CMN) server is set up as Azure VM
• VPN from Azure to on-premise
• Mail Connector fails to flow from O365 to Domino after a period of time
• Errors similar to the following are seen in the CMN log:

2013-11-05 14:43:43,763 WARN  CMN.logging [Proxy 106] - Message Number [106] on Thread [15] from Exchange (207.46.163.157:58504) to Domino (10.10.10.10:25): A communications failure or interuption was encountered. - IOException: Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond

Set the MTU or MSS on your device to 1350 or lower as mentioned in the MS template script for the VPN/firewall configuration:

# ---------------------------------------------------------------------------------------------------------------------
# TCPMSS clamping
#
# Adjust the TCPMSS value properly to avoid fragmentation
set flow vpn-tcp-mss 1350

For further assistance with this issue, please contact Microsoft Support.