Emails delayed AND missing from sent folder

Question

I am the admin of my tenant. One of my users is facing problems when sending emails, but the problem occurs only on a few cases for which I do not see a pattern:

The case that his sent or forwarded email (to several recipients) will be delivered to some but delayed to others, AND it will not appear in their sent folder.

I can see the message delayed when tracing it, but Exchange admin center will not give an error or explanation. If I click on "go hunt for this message", I will be sent to the Defender / Advanced Hunting page... but with a 400 error code.

If I click explore, I'll be sent to the Defender Explorer page, but it will be blank.

Answer 1

Sorry for late reply, but after some observation and testing, I finally found that the root of the problem was at the user's smartphone.

They had loggin in and been using their M365 work email with some Samsung email app, which had some kind of very invasive antivirus (or whatever) which apparetly runs its own anti-spam or anti-virus rules. When the app was deleted from the phone, user's M365 email started working normally again.

Thanks for your attention anyhow!

Answer 2

Hello Konstantinos GSA,

Good day!

Thank you for posting to Microsoft Community. We are happy to help you.

Please note that when in outlook app you sent email, and you cannot see it in sent item folder please check your outbox folder first, sometime due to the network the emails go to outbox folder and if your network come back the emails can be automatically sent, or you need to do it manually.

Before we proceed, I would require more information to assist you better.

1. can you get the message headers from the recipient inbox and do the message header Analyzer Message Header Analyzer (mha.azurewebsites.net)? or just got the original message headers and shared the result with us via the private message see the picture below:

access the private message click on the icon

2. Please what happening when you use outlook on the web?

3. Please can you do the extended message trace csv file with us if you have done it if not, please do it and share the csv file via the private message

Please get back to us with necessary information, we’ll be glad to assist you further.

Appreciate your patience and understanding and thank you for your time and cooperation.

Sincerely,

Eben Ezer Tres | Microsoft Community Moderator