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):
| Setting | Value |
|---|---|
| SMTP Server | smtp.office365.com |
| Port | 587 |
| Encryption | STARTTLS (TLS) |
| Authentication | Required |
| Username | Full email address (e.g., [email protected]) |
| Password | Email password or app password |
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.
SMTP Settings for Different Use Cases
1. Outlook Desktop App
If you manually configure Outlook:
Server: smtp.office365.com
Port: 587
Encryption: STARTTLS
Authentication: Required
However, in most cases, Outlook auto-discovers these settings.
2. WordPress or Website SMTP
If you run a website and want to send emails through Office 365:
Use these details in your SMTP plugin:
Host: smtp.office365.com
Port: 587
Encryption: TLS
SMTP Auth: Yes
Username: Full email address
Password: App password (recommended if MFA enabled)
This is common for contact forms, WooCommerce stores, and membership websites.
3. Printers and Devices (SMTP Relay Option)
For printers or scanners that send emails:
You may use:
SMTP Server: smtp.office365.com
Port: 587
TLS: Enabled
Authentication: Required
Or configure SMTP relay via a connector in Microsoft 365 if authentication is not supported.
Alternative: Microsoft Exchange Online Direct Send
Microsoft 365 supports different mail flow methods:
Option 1: SMTP Client Submission
Uses smtp.office365.com (authentication required)
Option 2: SMTP Relay
Uses your domain MX record (no authentication, IP-based)
Option 3: Direct Send
Sends mail internally within your tenant only
SMTP client submission is the most secure and recommended option.
Do You Need App Passwords?
If Multi-Factor Authentication (MFA) is enabled:
You must generate an App Password instead of using your normal account password for SMTP.
This prevents login failures and increases security.
Troubleshooting Office 365 SMTP Errors
Here are common SMTP errors and solutions:
535 Authentication Failed
Incorrect username or password
MFA enabled but no app password
SMTP AUTH disabled in tenant settings
530 Authentication Required
SMTP authentication disabled for the mailbox
550 Relay Not Permitted
Trying to send from unauthorized domain
Incorrect SMTP relay configuration
Connection Timeout
Port 587 blocked by firewall
TLS disabled
How to Enable SMTP AUTH in Microsoft 365
By default, Microsoft disables SMTP AUTH in some tenants.
To enable it:
Go to Microsoft 365 Admin Center
Open Exchange Admin Center
Select Mailboxes
Click the mailbox
Enable “Authenticated SMTP”
This allows the mailbox to send email via SMTP.
Security Best Practices for Office 365 SMTP
To keep your email secure:
Use port 587 with TLS
Enable Multi-Factor Authentication
Use app passwords for applications
Configure SPF, DKIM, and DMARC
Avoid using basic authentication (deprecated in many cases)
Microsoft continues moving toward modern authentication for improved security.
Example Office 365 SMTP Configuration
Here’s a real-world example:
Email: [email protected]
SMTP Host: smtp.office365.com
Port: 587
Encryption: TLS
Authentication: Yes
Username: [email protected]
Password: App password
This configuration works for:
Outlook
Thunderbird
Website SMTP plugins
Custom applications
How SMTP Fits Into Microsoft 365 Email Flow
When you send an email using Microsoft 365:
Your device connects to smtp.office365.com
Microsoft authenticates your account
The message is scanned for spam and malware
It’s routed through Exchange Online
Delivered to the recipient’s mail server
All of this happens in seconds.
Office 365 SMTP vs Other Email Providers
For comparison:
Gmail SMTP: smtp.gmail.com
Office 365 SMTP: smtp.office365.com
Yahoo SMTP: smtp.mail.yahoo.com
Office 365 is preferred by many businesses because of:
Enterprise-grade security
Advanced spam filtering
Compliance features
Integration with Microsoft apps
Frequently Asked Questions
Is Office 365 SMTP free?
Yes, it’s included with your Microsoft 365 subscription.
Can I use Office 365 SMTP for bulk emails?
No. Microsoft limits daily sending to prevent spam. For bulk emails, use dedicated services.
Does Office 365 allow anonymous SMTP?
Only through properly configured connectors (SMTP relay), not through smtp.office365.com.
Final Thoughts
The SMTP settings for Office 365 are smtp.office365.com, port 587, TLS encryption, and required authentication. These settings allow secure email submission from clients, websites, and applications through Microsoft’s cloud infrastructure.
Understanding these settings is essential if you:
Configure Outlook manually
Set up website email sending
Connect printers or devices
Troubleshoot email delivery issues
Microsoft 365 makes email delivery secure and reliable—but correct SMTP configuration ensures everything works smoothly.
