I am a remote working and I travel. Travel has been sparse this year for obvious reasons. But sometimes I have to work tethered to a cellular hotspot, and the last handful of times I was eating through my data like crazy. My company uses OFC365 and I have a local copy of Outlook with Cached mode enabled. There are a couple shared mailboxes mostly for calendar scheduling, and my mailbox is about 2-3GB in size.
I was getting notified by my cellular plan that I as about to run out of data. This never happened before, I've been traveling remote and using Outlook in cached mode for years.
I found this article which seemed plausible: https://docs.microsoft.com/en-US/outlook/troubleshoot/data-files/by-default-shared-mail-folders-are-... But it didn't seem to do much of anything after I set it to 2007 behavior. Then, I started investigating while at home on my home network. Using the performance monitor in task manager, looking at the ethernet adapter, with Outlook open I could see about 10Mbps traffic constantly. When I shut down Outlook, it would stop. I checked my network router traffic logs and found out that I was using about 100GB of outbound data traffic every day that I worked from home since about January 2021. Before January 2021, it looked normal. Was there an update in January this year that messed with Outlook? I have been using this laptop with this Outlook for two years.
The final solution so far that seems to have fixed is: In Outlook, delete the Office365 account. let Outlook delete the entire cache file. (takes a while) Close Outlook, restart Outlook, then re-add the same Office365 account to my profile. Let Outlook download all 2.8GB of the mail box (takes a while), and then later when it finally settled down, My network traffic even with Outlook open was back to nothing virtually.
What gives with these major disastrous issues? Like good ol' memory leaks? Win7 log files that eat up an entire drive, really? What normal person would be able to figure out an issue like this? It's terrible. We have a hard enough time chasing down third party malware, but Microsoft shouldn't be adding to the confusion. I can't be the only one that this happened to. There's got to be literally millions of OFC365/Outlook users.