The server responsible for this critical function is the Microsoft 365 SMTP server, which acts as the digital post office for outbound mail. These failures usually stem from configuration mismatches or security policies blocking the traffic.
Fix 550 5.7.1 Microsoft 365 SMTP: Causes and Solutions
Verify Port Settings: Ensure that the port is set to 587 and that the connection type is set to TLS or STARTTLS. Setting Value SMTP Server smtp.
This is typically achieved using the same credentials that employees use to log into their Outlook web interface or corporate email client. Alternatively, port 25 is often used for server-to-server relay between mail servers, although many cloud providers restrict its use for third-party applications to combat spam.
Fix 550 5.7.1 Microsoft 365 SMTP Server Error
Port 587 is the industry-standard choice for message submission and is recommended for most use cases, as it explicitly signals that the client intends to send mail. Server Addresses and Ports The hostname for the service is typically `smtp.
More About Microsoft 365 smtp server
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