PROBLEM:
Having defined a valid LDAP set that works for user authentication, when using it to retrive valid email addresses the error “No valid emails retrieved! Cross check you have added the relevant domain under System->Relay” is returned.
SOLUTION:
If the LDAP sets DN and Base DN are correctly defined, and if the domain is present in you Relay Domain list under System->Relay, check the Email Field in your LDAP entry is lowercase! Microsoft AD doesn’t like uppercase during queries, so be sure is set to “proxyaddresses” all lowercase.