Odd Behavior in Mail App: Running 10.11.6

[hapycampr2002]

In the 15 or so years I've been using Mac's I've never run across this odd behavior. I have no idea what I did in Mac Mail preceding this behavior. I have six or seven accounts in my mac mail. With one account - and it is only in one account - when I click on the "Compose new message" icon the new message field opens and extends far beyond the edge of my monitor. I have attached a couple of photos to illustrate. I have dual monitors, and the field stretches just beyond both cinema displays.

 

[Gregg2]

Temporarily change your monitor resolutions and resize it, then go back to the original resolutions.

 

[hapycampr2002]

Thanks Gregg2. That didn't help. It is only a problem in one of the seven accounts I have. I may be wrong, but that seems to indicate it is something specific to the Mail app, not outside of it. Also, I cannot resize the window horizontally (I can't make the window narrower), I can only resize it vertically (make the window shorter).