Applescript to create outgoing message in Mail.app with specified sender
From here

Slightly different format for the sender property.


tell application "Mail"
  set theOutMessage to make new outgoing message with properties {visible:true}
  tell theOutMessage
      make new to recipient at end of to recipients with properties {address:"first@mail.com"}
      set sender to "FirstN LastN &lt;josh.stackexchange@gmail.com&gt;"
      set subject to "Message Subject"
      set content to "Message Text"
  end tell
end tell



So yours would be...

tell application "Mail" to make new outgoing message with properties {sender:"FirstN LastN &lt;my@email.address&gt;"}


You can find and edit the FirstN and LastN in System Preferences>Internet Accounts>[Email Name]>Details>Name