I am running Windows Server 2008-R2 and Exchange Server 2010.
A co-worker, running Outlook 2010 on her office computer, sent an email to 6 recipients.
5 recipients received the email
1 did not receive the email, and sent this message:
host388.hostmonster.com #550-Please turn on SMTP Authentication in your mail client. mail.abcde.com 550-[nnn.nnn.nnn.nnn]:10188 is not permitted to relay through this server without 550 authentication. ##
How can I solve this problem?