My client has been using the email gateway for some years now.
About 6 months ago my client reported that emails would not send, they received a message saying Cannot send this item.After investigating I found it related to long URL's, once an email chain gets so long the links block the reply emails being sentWe use TOC via the email gateway, this is the cause of the issue as it rewrites the URL every time an email is sent even though it rewrote them previously.MS released a fix for this in April:https://www.bleepingcomputer.com/news/microsoft/microsoft-fixes-outlook-cannot-send-this-item-email-bug/This didn't resolve the issue my client is having, the fix may have been for 365 TOC.I have logged cases with support but not got anywhere, has anyone else seen this problem?
Seeing this come up more and more with end users as well.
I have added the URLs found in our companies signatures, hopefully that will help minimize this issue.
I have had to turn Sophos TOC off due to too many users having problems.
I had turned off the URLs for links in our signatures, but now with our TOC off, I see replies coming from outside partners where they are re-writing with their own TOC - which then would be re-written again by Sophos TOC. I'm going to try adding safelinks.protection.outlook.com to our safe list and see if that might help for outside parties that use Microsoft ATP.