Error: SMTP Error 449

What's Causing This Error

This error is a routing error specific to Microsoft Exchange Servers. Unfortunately, not much information is available on the possible causes of this error. Still, the Microsoft community has identified that a leading cause for this error is when a message is sent to a member part of a routing group that does not exist.

Solution - Here's How To Resolve It

There is no proper way to fix this, instead involves a series of trial and error. Microsoft recommends using their tool - WinRoute, to diagnose and resolve the error.