Our friends at Zen Software posted about an issue with Malwarebytes false positives causing some DKIM issues for MDaemon. What may happen is that MDaemon may start blocking all inbound email because it’s seeing false results that a DKIM message check has failed. This is not an MDaemon problem. What’s happening is that the libdkim.dll file that MDaemon uses as part of the DKIM check is being blocked by Malwarebytes. The solution is simple. Simply exclude the MDaemon directory from real-time or scheduled antivirus checks.
You can read the original post here on Zen Software’s blog.