When trying to test and email account on AD Audit plus the following is displayed 

Sorry, the page you requested was not found.
Please check the URL for proper spelling and capitalization. If you’re having trouble locating a destination.

Fix 

Pretty silly buy but : The allowed characters are down below:

0-9,a-z,A-Z_,-,.,$@,?,,,:,’,/,!,[,{,],},,,|,;,`,~,#,%,^,,*,(,),+,=,”,&,{InBasicLatin},”space”