550 5.1.1 User unknown when sending to distribution group Exchange 2010 Posted on February 10, 2014 by timdotexe EMC Distribution Group > Mail Flow Settings > Message Delivery Restrictions Uncheck ‘Require all senders are authenticated” Source: Microsoft Share this:Share Click to share on X (Opens in new window) X Click to share on Facebook (Opens in new window) Facebook Click to email a link to a friend (Opens in new window) Email Click to print (Opens in new window) Print
