I used Google with several keywords before posting here but probably used the wrong ones.
Thank you TheLastSuperman, I think it was the second one which you found here on vb.org but it's not present anymore.
However, we just got notice from our user that he got the email begin last year but only now reacted to it. LoL.
So now I understand how it could be that he got this message. Never thought a user would wait almost 2 years before reacting to such notice.
Problem solved, thank you all!