This week, I was working on an issue that caused me to scratch my head.
Issue was, user R (recipient) complained, that he started to receive e-mails from various senders he does not know and does not do business with.
After checking some samples of e-mails from the sent items folder in the senders mailboxes, I realized, user R was in the To or Cc lines of the mails that were sent.
Certainly, the issue happened infrequently and the senders varied.
So, the golden question was, how did user R get onto the To or Cc lines on those mails.
Similar issues are described here, e.g.:
https://social.technet.microsoft.com/Forums/lync/en-US/fbd34bb5-442c-46c9-b131-7920b59f4722/unintend...
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_outlook-mso_win10-mso_365hp/outlook-2016...
Thanks to my co-worker Rahul, who gave me the hint to check for incorrect AD properties of the recipient, and there it was:
Get-ADUser UserR -Properties *
[…]
ObjectClass : user
ObjectGUID : cf55f28a-ce78-4078-b9e6-d2326b58257f
otherTelephone : {,}
[…]
The AD property otherTelephone contains the unexpected comma character.
This customer has the otherTelephone property included in ANR resolution, so if a sender in Outlook mistakenly types the comma into the To or Cc field, it will get resolved against User Rs e-mail address.
This totally explains the issue where the recipient user R unexpectedly got e-mails from people he does not do business with and was on the To or Cc lines in the senders Sent-Items.
