Third Party SMTP with Gmail

Finally... Gmail's custom 'From:' feature lets you use Gmail to send messages with another of your email addresses listed as the sender in place of your Gmail address. This way, it's easier to manage multiple accounts from the Gmail interface.

From Official Gmail Blog.

This will help if you use one mail account as an aggragator for all your other email accounts.

Here is how to set it up: Adding a custom 'From' address