How can I configure Mail to delete these draft messages once the final message is complete and sent?
The problem you’re experiencing is a common one for users of both Apple Mail and Gmail. As we mention in our How-To Guide for Setting up Gmail and Apple Mail, a difference in the way that Gmail and Mail handle draft messages causes many duplicates to be stored and retained when Mail is configured to keep copies of drafts on the server. Therefore, despite its potential convenience, we recommend that Apple Mail users configure the software to only store drafts on the local computer.
To change the way Mail stores draft messages, open the application and go to
Mail > Preferences > Accounts. Select your Gmail account from the list on the left, and then select the “Mailbox Behaviors” button on the right. Uncheck the box “Store draft messages on the server.”
Mail will still keep frequent drafts of your sent messages as you compose them, but they will not be stored on Gmail’s servers and will only be accessible by the local computer on which the message was created. This means that if you begin to compose an email on your laptop but wait to send it, you won’t be able to access what you’ve written thus far from another device, such as your iPhone.
On the plus side, you’ll no longer have hundreds of draft email messages cluttering your search results.
Keep in mind that this configuration is due to a specific issue with Gmail. Other IMAP email services, such as Apple’s iCloud, function normally when draft messages are stored on the server.