Strange issue I’ve never seen happen in our exchange environment today. One particular email was sent in (legitimate) but anyone who replied got #550 5.1.3 STOREDRV.Submit; invalid recipient address #SMTP#... The email address was email@example.com. I noticed if we typed “firstname.lastname”@windriver.com it worked. Our entire internal naming convention for our company is firstname.lastname@example.org so why would exchange choke on the above address and require the “” around the name? Any ideas?