You shouldn’t have any need to receive email or gmail from a buyer in a normal gig situation. If they want to deliver files to you they should do it through the Fiverr system. It the files are too large they can use Dropbox or another service that lets you share files without email authentication.
If a buyer sends you an email address without prompting, don’t use it and don’t respond with any mention of the word email. Just tell them that you need to exchange files/info through Fiverr or give them an alternative like Dropbox. If you allow or ask a buyer to give you email or if you use the email, it is likely you will be banned.
There are rare circumstances where Fiverr will make exceptions. I had a gig once that required me to provide buyers with email addresses after doing research on certain things. I had to get permission from Fiverr in advance to deliver email addresses. There are few reasons that are really necessary, though.