Greetings. I will try to keep this as short as possible.
The business has two separate premises, one across the road from the other. The two sites are connected via Radio Links. Each site runs on its own unique IP Subnet. The Sophos firewall in question is situated at Site A. Site B has an on-premises MS Exchange server, so traffic needs to pass to & from the two sites for emails to work at Site A. Firewall rules have been configured to allow this traffic (see attachments). The rule configured to allow traffic from Site A to Site B applies a masquerade so that the traffic hitting the Exchange server appears to come from the server’s local IP Subnet.
This always used to work perfectly fine, and it still does work most of the time, but intermittently and randomly, some users will experience that the connection to the Exchange server does not flow. For example, when synchronising Outlook folders, it will make no progress, or when sending an email, it will remain stuck in the outbox for some time (maybe approximately 30 minutes). However, during this time the user can ping the Exchange server successfully. Eventually the problem auto-resolves, and folders will update or mails will send out etc. Closing Outlooking and relaunching it to re-establish the connection to the Exchange, sometimes works as a temporary work-around to wake up the connection again.
Upon investigating the firewall logs we find the attached, as if the firewall randomly decides to block such traffic for certain users some of the time.
Could you please advise where we might start looking for the cause of this problem? Let me know whether / when you require more info.
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