Thanks for attaching a screenshot. You'll have to modify or delete any saved passwords on your Windows Credential Manager. Allow me to explain further.
Windows Credential Manager allows you to store login credentials that you use to sign in to websites or other software installed on your computer. Since you're often prompted to enter your username and password in Outlook, you'll need to delete the information in the Remove from Vault section on the computer's Control Panel.
In this case, I suggest reaching out to an IT expert for further assistance.
Just in case, I'm linking an article for future reference: QuickBooks Email Login has changed.
You shouldn't be prompted to re-enter your credentials the next time you're sending emails from QuickBooks Desktop.
Please let me know how it goes. I'll be here to keep helping. Take care.