[AC Question]

I wonder if there is a way to change the From address. At the moment, K9 seems to default to using the username that is entered into the SMTP settings for the account. I would like to change it. I cannot change the username because then the SMTP server won't accept the mail.

[Rukbat]

The From: header is the SMTP name for the account. As you say, if you change the header, the server won't accept the email. If you want a different From: address, create a new email account. (Even if the SMTP server accepted the change, the POP3 or IMAP server would probably reject the email as improperly formed.)