You have a Gmail account but want to switch to another one. Most people do this when they want to set up a “business” Gmail account or simply because they found an Gmail e-mail name they like better.
You could enable POP on the old account and retrieve the mail in the new Gmail account that way, but then the timestamps get all reset to “new” and the Sent Mail gets all screwed up.
Is there a way to migrate from one Gmail account to another while retaining all proper timestamps and Sent Mail?
Yes there is and this article will explain exactly how to do it.

Please
[...] Migrating Seamlessly From One Gmail Account To Another [...]
Hey Rich! Just the guy we all need for THIS popular issue:
Problem: I have 3 different youtube accounts, but one favorite (long story)…. now, I want all my videos to be under one account.
Question: How can I “migrate” if that’s the word, my other 3 you tube accounts (some associated with totally different emails too) to my favorite youtube account?
btw, some of the videos I no longer have on my hard drive or anywhere else, other than the youtubbe account I wish to delete!
Help?
It is not possible at present to migrate multiple YouTube accounts into one. You will instead need to use a utility like http://vixy.net/ to download the videos from the other channels, then re-upload to your primary.