Airmail Address Book
If you send a message to, or reply to, someone who is not in your Address Book, that email address is stored in Airmail. At times, you may want to find or take other actions with this address, such as deleting it, and Airmail makes it easy to do this.
Go to Menu > Window > and select ‘Address Book’ which will bring up the screen shown below. To find a contact you can search for ‘Name’ or ‘Email Address’.
Contacts that have the Apple Address Book icon beside them can not be deleted, but those contacts with the Airmail icon (shown in blue boxes) can be deleted. Click on ‘Info’ and select ‘Delete’.
Deleting Contacts from Composer
Please enter an address in the to field and then press return to get the address in blue color and then just click on the small down arrow and then choose the option from the dropdown menu as shown in the picture below.