Phantom mail rejection from address that was not included in original email

[burnmore]

Hi,

A user is getting the following bounce message without having included the users in the TO, C.C. or B.C.C. section.

Message:

-----------------------------------------------------------------------

mx.google.com rejected your message to the following email addresses:

xxxxxx@gmail.com
There's a problem with the recipient's mailbox. Please try resending your message. If the problem continues, please contact your email admin.

mx.google.com gave this error:
The email account that you tried to reach is disabled. Learn more at https://support.google.com/mail/?p=DisabledUser 1si4409220wrg.526 - gsmtp

-----------------------------------------------------------------------

Its like the gmail address is adding itself before the mail is sent. But its all done via the browser. I have run anti malware on the PC and have antivirus up to date.

I've checked the users forwarding rules in settings, but at a loss where to check next?

No other user is having this issue.

Thanks in advance for any assistance.

[#2]

@burnmore Hello! This should be related to the Autocomplete cache being corrupt if I understand your issue correct. It's only happening for one user when sending to a particular recipient? As far as I understand you're using Outlook on the web (?) so when creating a new email and typing the recipients name in the To: field. Hit the X to delete the cached entry before it's being populated in the To: field. Then start all over with a new email and type in the recipients name manually or choose the address from the GAL if applicable.

Hope it helps!

[#3]

Best thing to do is run a message trace: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/message-trace-scc?view=o...