The SMTP settings for Office 365 (now Microsoft 365) are: SMTP server: smtp.office365.com, Port: 587, Encryption: STARTTLS (TLS), and Authentication: required using your full email address and password. These settings are used to send outgoing email securely from email clients, applications, websites, and devices.

Now let’s explore these settings in detail, explain when to use them, and understand how SMTP works within Office 365.
 

Microsoft 365 SMTP Settings Overview

Here are the official SMTP settings for Office 365 (Microsoft 365):

These settings are used for SMTP client submission, which allows users and applications to send emails through Microsoft 365 servers.

 

What Is SMTP Client Submission?

SMTP client submission is the most common method for sending email from:

• Outlook desktop

• Mobile mail apps

• WordPress websites

• CRM systems

• Multifunction printers

• Line-of-business applications

When you use smtp.office365.com on port 587 with TLS encryption, your email is securely transmitted to Microsoft’s servers for delivery.

Why Port 587 Is Recommended

Port 587 is the standard port for secure email submission. It:

• Requires authentication

• Uses TLS encryption

• Prevents open relay abuse

• Ensures compliance with modern email security standards

Port 25 is often blocked by ISPs and cloud providers, so Microsoft recommends port 587 for most configurations.

Encryption: STARTTLS Explained

STARTTLS upgrades a plain-text SMTP connection into an encrypted one. This ensures:

• Credentials are protected

• Email content is encrypted during transmission

• Protection against interception attacks

Microsoft 365 requires TLS encryption for authenticated SMTP connections.

Read More: What Are the SMTP Settings for Office 365?