Can you be more explicit about what you mean when you describe "******@g.com" as a "bad e-mail address"?
There is nothing "wrong" with that SMTP address except that it may not belong to a valid domain, or that the user portion of the address doesn't exist in the mail system that is responsible for the domain.
If "g.com" is a domain managed by your Exchange organization you can verify that the address is assigned to some sort of mail-enabled object by using this:
Get-Recipient ******@g.com
Checking an e-mail address to see if it's properly constructed is not difficult, but it does involve checking the user portion for extraneous characters and the presence of consecutive "." characters. The domain portion can be checked by looking for the MX record(s) for the domain.