Have had this issue for a while and would be REALLY good to try and find a way to finally fix it.
Sophos SG135w UTM9 running 9.510-5 fw. LAN interface for wired PC's (less than 35) connections running Outlook 2013/16 to hosted email with Rackspace. Web filtering is set to Transparent mode with Active Directory SSO as the Default authentication (I do have a couple of users on the Skip Transparent Mode Source/Destination list which doesn't seem to make any difference with this problem) and also is an outgoing LAN/Any IPv4 firewall rule for a couple of PC's, which I setup to see if that helps.
We use Cached Mode in Outlook (12 months) and when it comes to updating someones PC or new Outlook install it can take hours or even days to download the emails etc for cached mode. Which can cause everyone else Outlook to either slow down, grind to a halt or just stop connecting.
So I want to know if there is a way that I can make the UTM9 stop filtering or stop slowing down email access? Had this problem for a while and the past couple of days email access for most people has been patchy at best. This doesn't always affect everyone, but still it would be fantastic to make the firewall route the traffic out properly so it's not so slow, there shouldn't be any reason why it is this slow, its not like its a massive network, and its not the internet connection that is slow as I can quite happily download big files as full speed while the email trickles along.
HELP!!!
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