Right click the account, select Settings and. Change it.

I don't see where it says Val Professional. I did what you said and this is what I see

Do you have an entry for your address in any of your address books?

yes but none of them say Val Professional anywhere.

Your screenshot shows 2 accounts. I guess you checked both of them?

Did you enter anything under Identities in Thunderbird?

Just the regular stuff that was in the screen shots I showed previously.

There has to be another location, probably when I first set it up, but it was ages ago, so I can't remember. I only noticed this problem a few days ago.

what is your user name as hostmoster? ValProfessional perhaps or something you have in settings there. IT is not unusual these days for outgoing server to actually change that information as the mail is in transit. Outlook and Gmail also do it.

girasole9 said

Just the regular stuff that was in the screen shots I showed previously. There has to be another location, probably when I first set it up, but it was ages ago, so I can't remember. I only noticed this problem a few days ago.

Your screen shot does not show the Identities screen. Click the button labeled Manage Identities and see what is there.