Mail uses wrong sender from Smart Mailbox

I am using Apple Mail on macOS Tahoe with multiple email accounts. When composing a new message, Mail is set to “Automatically select best account.”

Previously, I was viewing all messages in a combined inbox and often sent emails from the wrong account because I did not notice which sender account was selected. To address this, I created Smart Mailboxes to display inbox messages for each individual account.

This worked briefly, but now when I select a Smart Mailbox and click Compose, Mail consistently uses the wrong email account as the sender. However, when replying to an existing message, the correct account is used.

My understanding is that the selected mailbox should influence the sending account, but this does not appear to apply to Smart Mailboxes.

Why does this occur, and how can I ensure the correct account is used when composing from a Smart Mailbox?