Well first we need to know what email are you using, the stock app or something like Dolphin, K9 etc. Also, are you talking about gmail, AOL, Hotmail, Comcast (or other cable provider) etc. Corporate or exchange email are a whole different story. Need more information.
I might be able to help you with gmail, but I don't use Yahoo so may not be of much help. I have read a number of threads with people having problems with the Yahoo email client, not just on the Razr. I think there is a good thread on the Moto Support Forum for the Razr that talks to the Yahoo issue...suggest you check that out. Now, for gmail...you should not have to set your phone up to check gmail...gmail is push to your phone from the gmail servers...you should not have to do anything. If you don't want gmail to push the gmail to you go to menu>settings>accounts>select gmail account and uncheck the sync options you don't want.
On your Droid 3 go to menu>setting>accounts and select your gmail account and turn off sync for email.
