Whoops, thanks for the help!
Switching to the correct test revealed the actual error to be caused by a 403 response while testing the FolderSync command. Looking at the sogo-mailcow logs I see the following:
52.109.8.10, 52.109.8.10 "OPTIONS /SOGo/Microsoft-Server-ActiveSync HTTP/1.0" 401 0/0 0.002 - - 0 - 11
52.109.8.10, 52.109.8.10 "OPTIONS /SOGo/Microsoft-Server-ActiveSync HTTP/1.0" 200 0/0 0.002 - - 0 - 11
<0x0x55886700d5e0[SOGoActiveSyncDispatcher]> EAS - Forbidden access for user (null)
52.109.8.10, 52.109.8.10 "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=FolderSync&User=test@emailexample.com&DeviceId=30215491&DeviceType=TestActiveSyncConnectivity HTTP/1.0" 403 0/13 0.003 - - 0 - 11
Do you have any suggestions on how I might be able to fix this issue?
Thanks