I suggest you check the entries you have in your address book for HotelMaven I think you will find one with billsteiner@duck.com as the email address.

Thunderbird uses the name from your address book as a first choice of display name, however I disable that in settings as I want to see the name the sender placed in the email.

Thanks Matt, that worked, although I don't know why it started being an issue all of a sudden. 2nd issue is asking for my password when I log in. Any ideas? Thanks again.

Is it asking for your account password or a primary password?

In the case of a general password request, perhaps have a look at what is stored https://support.mozilla.org/en-US/kb/password-manager-remember-delete-change-tb

I could wax lyrical on passwords for a long time, but I will limit this to there can be password issues when antivirus products are allowed to scan mail. In the first instance try disabling any email scanning.

If you have set a primary password, then there is only an option to remove it. https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password#w_removing-your-primary-password

Thanks Matt, that worked, although I don't know why it started being an issue all of a sudden.

A late response. The setting is enabled and disabled in settings. Search address and look for "Display name". I hace had mine disabled for years as I tend to have some odd stuff in my collected addresses and can't be bothered with the level of control that setting my own display names for folks provides.I am happy with what they set. If anything at all.