Where did this alias come from??

Thanks P. Phillips... That seems to have done the trick... Never had gone looking under the Window column before and was previously unaware of the "Previous Recipients" list... Perused that very long list and 3/4 of the way down I found an entry for "m" with my neighbor's email address listed next to it... And last date used showed as yesterday when I was playing with ways to delete that association. I first started another email just to see that the unwanted association was still there... It was... I then went to that entry on the "Previous Recipients" list, highlighted it and clicked on "Remove from list" where it disappeared immediately (with no confirm or any such)... For grins I quit Mail, restarted, opened a new email and started typing my neighbor's email address... NO MORE "m"... So how it got there to begin with is beyond me but that list must essentially be the "source" for any such alias... And I don't have this alias issue with any other of many, many email addresses I send emails to so I will write this one off to "one of those things"...

So thank you for pointing me to a list I had never seen before (even though I've used Apple Mail for a very long time), this "Previous Recipients" list... That seems to have fixed the issue...

Thanks much for your help...

So I found this (see attached screenshot) by doing a search of my computer for "m"... What does it even mean to see the phrase

"Siri Found in Apps"... ???? What does that even mean... And connected to that small message was a larger window which again show the letter "m" and in a part of the screen that I cut off intentionally for my neighbor's privacy, there was his spelled out address (the correct email address) just below where you see "FaceTime"... Again, I chopped that off....

And in the upper right hand corner of the window that opens in search that shows this "m" and the stuff about Siri, I see what appears to be the Contacts application icon... But if I open Contacts, there is nothing but two items that have no relationship to "m" or to my neighbor's email address...

So what does "Siri Found in Apps" mean??? Any help would be much appreciated... See screenshot...

Checked that... No... I don't use the Contacts app... It does have a couple of default entries with my name on them and my computer name but nothing else and certainly nothing that would point to "m"...

but finding the source of that alias was my issue.. See my related response where P. Phillips appears to have found that "source" in the "Previous Recipients" list that I was previously unaware of... Thanks for your input...

No, but I can... He is my next door neighbor... I will check but I'm still thinking it's coming from somewhere within my Mac...

Is there some Terminal command that can locate alias sources on a Mac, macOS Monterey 12.4...