According to a reader on Apple blog TUAW, Apple's email service is incorrectly filtering or actively deleting mail from bulk mail mergers like Constant Contact, Direct Mail and MaxBulk Mailer, among others. This means users who have signed up to receive newsletters or other promotional email blasts may never receive the mailings.
With the reported bug, emails sent through mail merger services are not bounced back and appear to be lost or deleted entirely without the knowledge of either sender or recipient. Curiously, the issue seemingly affects only HTML documents, leaving plain text messages untouched.
The publication says the problem has been ongoing for "at least a couple of weeks" and notes email headers may be to blame for the auto-deletion, suggesting the issue is on the server end.
While mail mergers can be used to create and send out spam, many companies rely on such services to dish out weekly newsletters, special promotional deals and other information opt-in subscribers may be interested in. Without a bounce back notice, legitimate vendors have no way of being notified that its customers are not receiving the mailings.
The alleged server-side handling issue adds to Apple's email-related woes. Since the release of OS X 10.9 Mavericks in October, Apple's Mail app has been plagued with problems seemingly tied to specific services like Google's Gmail. The company tried to fix Mail with December's OS X 10.9.1 maintenance update, but many users continued to complain of unreceived messages.
A standalone patch was released in February, while OS X 10.9.2 reportedly further improved Mail stability later that month. It appears that Mail is still not completely fixed, however, as the app remains as one of the few focus areas in the latest OS X 10.9.3 betas.