Most of us keep more than one email id. We may be keeping one for personal communication, one for business communication etc. But it is really difficult to keep up with multiple email ids. You have to check all these ids for any incoming message or to send any mail from those.
But now with gmail, you can completely manage your other email ids with a single id. For the case of incoming messages, you can set to forward all the messages coming to that id to your gmail id.(ie, if you configure to forward your emails, you can read emails sent to email@example.com from firstname.lastname@example.org). So the problem of incoming mail is saved for now. You can find the mail forwarding option in gmail >> settings >>forwarding >>
And if you want to send a mail from another account, that is also possible with gmail. In Gmail >> Settings >> Accounts >> , you can configure other email ids. Gmail will send a confirmation message and once you confirm the ownership of the other email id, you can start sending emails from those ids from your accounts.That is., if you set email@example.com to be your additional email id, then after confirmation you can send emails ‘from firstname.lastname@example.org’, right from the gmail id- email@example.com. Nice isn’t it?