I looked at yahoo and didn't like it.
I already have a gmail account and the simplest way for me was to let gmail take care of transferring everything. I did use mail forwarding from Cox but it wasn't needed. Gmail takes care of everything. You put in your Cox credentials and it starts transferring everything that was in your Cox inbox. No need for some ripoff $99 program that I saw while Googleling for instructions. Free and easy.
I also decided to change my email address with all the websites I normally use. I get so much junk/spam/phishing in my Cox email that maybe this will free me from a lot of it. It wasn't that hard. Just log in, go to your profile and edit your email address. Most of them will send a text code to verify, and then you're done. All my important websites are in my bookmarks, so I just went down the list, some 2 dozen businesses, banks, credit cards, etc.
If you want to simply transfer your Cox emails to gmail:
Start a gmail account with Google. Open your gmail and click the Icon Wheel (settings). then click "See all Settings." Look for "Accounts and Imports" then for "Import mail and contacts." Enter your Cox login info and BOOM, sit back and let it do the rest. Takes about a day for some 700 emails.
You might want to also get the Gmail app for phone, iPad, MacBook, etc, whatever you're using. Or just go to Google.