Could you post access protection log here?
You need to check the exclusion of the policy.
If you select the 'Prevent mass mailing...' line in the policy there's an edit button. Within that there is a list of process exclusions that are allowed to send emails.
Check to make sure these haven't change by comparing them to the 'McAfee Default' (read-only) policy.
If nothings changed them you'll need to look else where. e.g. have you installed or reconfigured any firewalls around the same time or maybe re-configured your mail server?