We are trying to setup a hybrid configuration for an specific domain. This hybrid configuration has several e-mail addresses which use our SmarterMail Server and other addresses use Office 365:
- MX DNS register are pointing to our SmarterMail server
- E-mail addresses hosted in Office 365 are setup like an alias in our SmarterMail server. This alias redirect the e-mails to the corresponding Office 365 account (for example: firstname.lastname@example.org redirects to email@example.com).
When we try to send e-mails from an e-mail account hosted in Office 365 to an account in our SmarterMail server (both e-mail accounts belong to the same domain in an hybrid configuration), we receive this bounce error:
"550 5.7.368 Remote server returned authentication required to relay -> 550 Authentication is required for relay"
So, the solution we have to apply is deselect the "Require SMTP Authentication" for the domain in the SmarterMail server. But this is a hole security in order to avoid SPAM sending through our SmarterMail Server.