Here's how you can transfer all your emails from one Gmail account to another:
Step 1: First, log into the old email account (account you want to import the emails
from) and click on
Settings, then
Forwarding and POP and choose
Enable POP for all mail. Click
Save Changes at the bottom.
Step 2: Now log into the new email account (account you want to import the emails
to) and click on
Settings. Then click on
Accounts and click on
Import mail and contacts button.
Step 3: Type in the old Gmail address in the text box and click Continue.
Step 4: Now type in the password and click Continue.
Step 5: Type in (if its a text box) or select
pop.gmail.com from
POP server dropdown list. You can also select Port 995, click on "Use SSL" and click "Continue".
Step 6: Select the options you need and click on "Continue"
Step 7: Now wait and watch all your emails getting transferred to the new Gmail account. If you have lot of emails it may take several hours for the emails to get transferred/imported.
Once the import has started you chan check the Import status/history in "Settings >> Accounts >> Get mail from other accounts >> View History".
Also there is no need for you to stay logged in once the mail transfer/import has started.