If you use multiple email services, you can set your Gmail account, so all mail ends up in your inbox. And you can send mail from any of the other addresses you own right from Gmail as well. There’re two steps: 1. Set up mail forwarding or fetching: Log into your non-Gmail account and set up auto-forwarding to Gmail address. If your non-Gmail account doesn't offer forwarding but supports POP3, use Mail Fetcher in Gmail to auto check other email account and download new emails to Gmail. 2. Set up Gmail’s custom "From:" feature lets you send mail with one of your other email addresses listed as the sender in place of your Gmail address (you can add as many addresses as you want). Once custom "From:" is set up, you can pick an address you want to reply from in the "From:" address drop down while composing messages.

Source:→ Gmail Blog