So it turns out there can be a glitch with Mavericks and Gmail. When I installed Mavericks on my Macbook Pro, all my messages piled up into my outbox, but weren’t sent. It turned out that Mail wasn’t picking up my password properly from the System Preferences. Here’s how I got it going.In OSX Mavericks you enter your mail settings in the System Preferences: Internet Accounts screen. It looks like this:
The Mail.app doesn’t seem to pick up all the settings to send mail properly, so you may need to put them in manually.
1. Go to the Preferences menu within the Mail App.
2. Click on ‘Account Information’ and down to the line that says Outgoing Mail Server (SMTP) and select ‘Edit SMTP Server List’
3. Now you will see a screen like this. This is where you need to re-enter your password.
Now your outgoing Gmail should work!