No it is not. You would need an md5 preimage attack to go from md5sum to email (what I assume you mean by 'brute force')

To prove my point, c5633e6781ede1aea59db6f76f82a365 is the md5sum of an email address. What's the email address?

If the attacker already knows a given input email ('[email protected]'), then any hash algorithm will identically let them see the emails.

The problem with the above proposal isn't related to hashing, it's that the email address is being used as a password to see sent contents, which seems wrong since email addresses are effectively public.