Alternate sender name appearing when I use Mail.app

I have used Mail as primary email app for years. Lately, I was hospitalized at a cancer center, with a lot of email coming from them. However, since that time and after being home, all my email from my Hushmail account (sent & received thru Mail) appears with the hospitals name as part of my sender address. See picture below. I do not work at or represent Fox Chase or its Repository, thus no reason for this:

How can I fix this ?

MP

p*****@hushmail.com\

[Edited by Moderator]