Outlook 2016 and its many connections to Office 365 Groups


If you examine the network connections opened by an Outlook 2016 client, you might find many connections established to the mailboxes belonging to Office 365 Groups. Using connections to grab data is fine, but why are the connections quite so persistent and what do they do anyway?


6 Replies

Oooh so you did get an answer on this? I asked it on the Outlook session at the Summit, didnt get much info. Do share on the list if there's more to it please :)

All I know is what I reported in the article. The Groups team know about the issue and will try and do something better over time.

OMG...thanks for sharing this Tony!!!
Great stuff Tony! I never noticed this. I work for large schools where we plan to deploy a whole bunch of groups based on other memberships (such as HR groups/teams, Project teams etc.) automatically. This may be something to keep an eye on. Thanks!!

I think the biggest concern around this is in situations where NAT is involved, as having that many open connections can easily cause port exhaustion. However, when I did the same test with 100 groups, quick check with netstat showed only a handful connections compared to normal Outlook usage, wile the Outlook Connections dialog was showing well over 100. The truth is somewhere in between I guess...

I suspect that some of these connections are used (to synchronize with a group) and then torn down after a period of inactivity in the group but they remain listed as active. On the other hand, some threads might reawake because some activity occurs in the group. There's no doubt that the picture presented by Outlook can overstate the real situation, but I shall leave it to the engineers to figure out.