MAIL is changing "sender" address

By design or intent, this is a flaw in Apple Mail for MacOS. For someone who works with multiple email accounts nearly every day, the two options for “Send new messages from:” are inadequate. The user can select a single default sender account, or allow the mail tool to “automatically select best account.” Choosing the latter allows the mail tool to somewhat arbitrarily make changes to the sender’s “From" account to one that is not intended and generally not “the best account” based what address is entered in the “To” field. It makes little sense. This limitation requires users with multiple mail accounts to constantly check their “From” address before sending to ensure any replies end up in an appropriate inbox.

I suggest Apple developers need to enable a third option “send from the current or active account” so that, for example, an email composed in the “XYZ.com" account actually sends from “XYZ.com" and not one of the other user’s accounts.

Probably a bug...I clicked on 'Mark addresses not ending with' in Composing, then unchecked it, and now 'Send new messages from:' is listing all my email addresses.