Outlook seems to be resending old emails

I work as an Exchange admin / Outlook support person and can confirm, I'm seeing this issue trending upwards over the last year or so, getting worse and worse over time. It's at its max right now with more and more users noticing the issue. The problem is, it's not always an easy to notice issue so it gets overlooked often (that's my personal hunch). The next problem is, Outlook's logging, mailbox audit logging, M365 Unified Audit Logging - all fail to capture the details other than the ones that make it look like the user used Outlook today to create and send the message.

I've seen cases where the impacted users had messages stuck in their Outbox. In those cases, sometimes, but not every time, the resent message(s) would be one of the ones within the set of stuck in Outbox messages. But not always.

Another common trait I've seen is that the messages are generated from MS Word, by going to File > Share > and sending the .docx as an attachment. In these cases, sometimes the subject is blank, and sometimes the subject is exactly verbatim the document file name. Sometimes, the resent message has the document file name for the subject, but the original sent message had no subject. Again, it's not a Word-source email in all cases I've seen. I did noticed that both @Gerard Vanhaver and @James Millward pointed out that they saw this issue relating to MS Word / MS Excel. Slightly different use case in either's report, but still in line with what I've described just above. Like, is this some kind of problem stemming from New Outlook new gracefully jiving with traditional rest-of-the-Office-suite of apps? Sure looks like it to me.

In many of the cases, the users have or are using New Outlook. These issues certainly popped up well after "New Outlook" was revealed with the slider to try it.

I think the mechanism that make the "Undo Send" feature possible, might be related to this issue. I've had some users find their "Save sent item to" setting mysteriously set to the Drafts folder, even though they are sure they never set it that way. The only thing I know of that does that behavior is the "Undo Send" feature. Right now I'm advising impacted users to consider changing the Undo Send feature from 10s to 0s to try and disable it. This is just a theory.

I've had one case with MS Support and it proved to be impossible for them to support. Since the issue cannot be reproduced on demand, and since all the evidence erroneously paints a fictious story, we had no way to prove that we even have a problem. But now that we have so many reports of this issue, and because the internet doesn't lie and we see tons of other people raising this issue, we're re-opening our support case.

If anyone can share any insights, or even just chime in to try and show the number of people facing this issue, that would be great.

Hello Cece,

I am experiencing the same issue. Please message me so I can resolve this ASAP. This is an account for a business and needs to be resolved immediately.

Hi, WellyPhil

Thanks for you response!

Since there is no unusual activity on your account and the 4 emails that were randomly sent are appearing normally in the Sent folder.

It does seem strange that this is happening, and I can't think of a reason for this problem, either. Could it be that the 4 randomly sent emails have something in common? But why are they being re-sent???Haha, it is truly strange!

Can you share the emails in question with me via private message and see if can figure out why in particular:

①    You can send private message through the Messages link at the top right of the page. 

②    Check your sent PM by going to My Profile, and then selecting View private messages on the left pane of your profile page. 

Thank you for your cooperation and support!

Best Regards,

Cece | Microsoft Community Support Specialist

Good morning (NZ time) Cece, thanks for getting back to me so promptly. There has been no unusual activity on my account, and indeed the 4 emails in question are in the Sent folder in outlook.live.com. So I am still baffled as to how these emails were resent ...

Cheers, Phil

Hi, WellyPhil

Welcome to Microsoft Community.

I realize that you've encountered a problem with old emails be send.

According to your description, On one hand, your old emails are being resent for no reason, and on the other hand, the footer of the resent emails does not match your actual email client.

Therefore, please log in to Microsoft account website account.microsoft.com, and in the [Security] page, click “View My Login Activity” to check whether there is any unauthorized access.

In addition, please log in to the website outlook.com and check if the 4 randomly sent emails exist in the Sent Mails folder.

Of course, you can also contact the recipients of the emails and ask them to check if there are any anomalies in the origin of the emails.

Thank you for your cooperation and please let me know how it goes!

Best Regards,

Cece | Microsoft Community Support Specialist