Want a quick way to switch between email identities when sending email in Apple Mail? Well it’s remarkably easy – once you know how!
Instead of creating separate accounts, simply add all the email addresses separated by commas on the email address line in Mail > Preferences.
Mail.app will then display a drop down list of the addresses next to ‘From’ when you compose a message. Just pick the one you want and away you go. Don’t forget that if you are using an address not provided by your ISP then you may need to use SMTP authentication to prevent anti-relaying from blocking your outgoing mail as spam.