I have two accounts, a gmail one and a school email address. I want to be able to send emails from my school address and gmail, but receive only from the gmail one (the gmail and school email accounts are synced together so I don't want to get duplicates). is there any way to make only the receive section of an account offline in Mail.app? I'm using OS X 10.9 Mavericks, if that helps. I already turned off automatic receiving for my school email, but if I hit "get mail" all the email from that account gets fetched anyway.
Set up a new empty email box (perhaps with server side quota or rules to delete all mail immediately upon receipt).
Enter those credentials as a new account in Mail.app and end the sending credentials and server for this shell account.
Now you can send from the account you want and have no emails coming in.