Overriding the "From" field

To set a custom email address and sender name on a message you intend to send, enable View ▸ From Override Field and change the default sender name and email address in the corresponding fields.

This functionality can be useful for wildcard mailboxes when using qmail and sub-addressing.

Setting an arbitrary address might collide with your email provider's Sender Policy Framework and/or DomainKeys Identified Mail restrictions.