Exchange Connection Problems

Which SMTP Port Does Microsoft 365 Use: 465 or 587?

Tauseeq Magsi Oct 8, 2026 870 views

Question details

The user needs to determine the correct SMTP port for sending emails via Microsoft 365, specifically choosing between port 465 and 587.

Which SMTP Port Does Microsoft 365 Use: 465 or 587?

Product: Microsoft 365
Device & OS: not provided
Scenario: Configuring an email client, application, or network device to send outgoing emails using Microsoft 365 SMTP servers.
Observed behavior: The user is unsure which port to use, noting that some devices default to port 465, but Microsoft documentation recommends port 587 for SMTP AUTH client submission.

Before you start

Ensure you have administrative access to your email client or device's network settings and have your Microsoft 365 account credentials ready.

Solution 1Recommended

Configure Microsoft 365 SMTP Using Port 587

Port 587 is the officially supported port for authenticated SMTP client submission in Microsoft 365. You should configure your client to use this port with STARTTLS encryption.

Microsoft 365 client SMTP submission generally uses port 587. If your device recommends or defaults to port 465, it may not support SMTP AUTH client submission properly for modern Microsoft 365 environments.

Access Email Server Settings

Open your email application or device's network configuration and navigate to the Outgoing Mail Server (SMTP) settings.

Enter the SMTP Server Address

Input 'smtp.office365.com' into the outgoing mail server address field.

Set the Port and Encryption

Change the port number to 587. Ensure the encryption method is set to STARTTLS or TLS.

Enable SMTP Authentication

Check the box for 'My outgoing server (SMTP) requires authentication' and enter your full Microsoft 365 email address and password.

Configure Microsoft 365 SMTP Using Port 587

Port 465 Support: Port 465 is a legacy SMTPS port and is generally not supported in the standard Microsoft documentation for modern Microsoft 365 SMTP AUTH client submission.

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Frequently Asked Questions

Why does my device automatically default to port 465?

Many older devices, printers, and legacy email clients default to port 465 for SMTPS (SMTP over SSL). However, modern protocols used by Microsoft 365 rely on port 587 using STARTTLS.

What happens if I try to use port 465 with Microsoft 365?

If you use port 465, your device or application may fail to authenticate or connect properly, as Microsoft 365 primarily supports port 587 for SMTP AUTH client submissions.

Do I need to enable SMTP authentication in my Microsoft 365 admin center?

Yes, to use SMTP client submission (port 587), 'Authenticated SMTP' must be enabled for the specific mailbox in the Microsoft 365 admin center.

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