USER wasn't found at MYDOMAIN.COM - Emails bounce back
I have added two email accounts for our staff (dedicated personalized accounts) under our main domain. But when I try to send an email to these sub-email accounts - I instantly get en error in Outlook saying:
"We won't be able to deliver this message to USER@MYDOMAIN.COM because the email address in no longer valid"
Any knows how to fix this? We have added these sub-email accounts to out iOS devices without any issues, so we dont understand why the emails bounce back.