Official Gmail Blog: Tips for importing old email to Gmail
"how to retrieve your mail from old accounts using POP" .
1.Go to Settings >> Accounts >> Get mail from other accounts >> Add another mail account
Fill the form click"Next Step." with port 995
click on "Add account" and select "yes"
Sending mail from your old address USING NEW GMAIL ACCOUNT .
Settings >> Accounts >> Send mail as: >> Add another email address.
Click on "Next Step" and then "Send Verification."
You will receive an email with instruction on how to validate your old email address
After set up being done, select this address in the "From" field when you replying/forwarding.