:587 a plain text password file cannot be used in postfix directly. Save the username and password for authentication on Microsoft 365 SMTP to a file /etc/postfix/sasl_passwd. System mail name -> your FQDN ( hostname -fqdn).General type of mail configuration -> Internet Site.When configuring the postfix initial setting, set: Sasl2-bin – is the Cyrus SASL API implementation that allows using authentication in postfix. You can also enable SMTP authentication for EOL user through the Microsoft 365 Admin Center: Users -> Active Users -> select a user, go to the Mail tab and click Manage email apps.

In our case, it is enough to enable SMTP AUTH for a single user account using PowerShell: Set-CASMailbox -Identity -SmtpClientAuthenticationDisabled $false Connect to your Exchange Online tenant using the Exchange Online PowerShell v2 (EXO v2) module: Connect-ExchangeOnlineĬheck the SMTP authentication settings for the tenant: Get-TransportConfig | Format-List SmtpClientAuthenticationDisabled So you need to enable SMTP AUTH (basic authentication) for the user under which your postfix will be sending emails.īy default, SMTP AUTH is disabled at the level of the entire Exchange Online tenant. Enable Authentication in Microsoft 365 (Exchange Online)īy default, postfix only supports basic authentication for users in Microsoft 365. Then you need to configure postfix so that it authenticates to the Microsoft 365 SMTP under a user account and sends emails. For example, instead of setting up a Microsoft 365 SMTP connection on every device on your network (network printer, all-in-one/ multifunction devices, scanner, etc.), you can set them all to send emails to the postfix SMTP host on your local network. Smart host is most often used as a single service for sending/forwarding email messages from the local network to an external email server.

365 smtp setting