User Account vs Distribution Group

We have discovered a problem in our AD which was managed by previous IT Mgrs.

Do you agree with statement below - why and why not?
Any account used for ONLY email purposes should NOT have a user account in AD instead they should be in their own Distribution Group in AD

We want your opinion - these accounts that were created for email are never logged into by any of our users. Were talking more than 10 of these accounts.