We've previously walked you through how to import old emails from other clients to Gmail using IMAP, or you can do it using POP. However you imported your old mail,
Google support page runs you through how to set up Mail Fetcher. The last step is "Add Account". At this point:
- * label incoming mail "imported" so it's easier to search for later if you need to
- * once you've validated the new account, select "Yes, I want to be able to send mail as [email protected]"
Olivier says this will let you use the "from:me" search in Gmail to look for email you sent using any name or address - so you can find everything you sent from all your old addresses and aliases.
If you still want to send mail through Gmail which looks like it's from your old email address you can set up a custom "From:" so that you can select this address in the "From" field when creating an email or reply in Gmail.
- * go to Settings > Accounts > Send mail as: > Add another email address.
- * Click on "Next Step" and then "Send Verification." You'll receive an email with instructions on how to validate your old address.
- * Once it's set up, you can select this address in the "From" field when creating a message or reply by clicking "change" next to your address in the From field.
Tips for importing old email to Gmail [Official Google blog]