Setting up Office 365 SMTP correctly is essential for sending emails securely from Outlook, applications, printers, scanners, and third-party tools. The correct Microsoft 365 SMTP server is smtp.office365.com, using Port 587 with STARTTLS encryption and required authentication.
In this guide, you’ll learn the complete Office 365 SMTP settings, how to configure SMTP authentication, troubleshoot common sending issues, and understand the difference between SMTP AUTH, SMTP Relay, and Direct Send.
Office 365 SMTP Settings (Quick Configuration)
Use the following Office 365 SMTP settings to configure email sending from Microsoft 365 applications, email clients, printers, scanners, and third-party tools.
Setting | Value |
|---|---|
SMTP Server | smtp.office365.com |
SMTP Port | 587 |
Encryption Method | STARTTLS (TLS 1.2 or higher) |
Authentication | Required |
Username | Your full Microsoft 365 email address |
Password | Microsoft 365 password or app password (if MFA is enabled) |
SMTP AUTH | Must be enabled for the mailbox |
Recommended Authentication | OAuth 2.0 for modern applications |
The correct Office 365 SMTP server is smtp.office365.com. Microsoft recommends using Port 587 with STARTTLS encryption for secure email submission. SMTP authentication is required when sending emails through Microsoft 365 using applications, devices, or email clients.
If you are configuring a printer, scanner, CRM, or custom application, make sure SMTP AUTH is enabled and your device supports modern TLS encryption for a successful connection.
Understanding Office 365 SMTP Basics
What is SMTP?
SMTP (Simple Mail Transfer Protocol) is the standard protocol used to send outgoing emails across the internet. In Microsoft 365, SMTP allows users, applications, and devices to send messages through Microsoft's mail servers securely.
When you send an email from Outlook, a CRM platform, a printer, or another application, SMTP handles the connection between your account and the recipient's mail server.
How SMTP Works in Office 365
Office 365 SMTP uses the server smtp.office365.com to process outgoing email requests. Before messages are delivered, Microsoft verifies the sender through authentication and encryption requirements to help prevent unauthorized sending and improve email security.
SMTP is commonly used for:
Sending emails from Outlook and other email clients
Connecting business applications and CRM platforms
Configuring printers and scanners for scan-to-email
Sending automated notifications from servers or software tools
A correct SMTP configuration ensures reliable email delivery, reduces connection errors, and helps maintain a trusted sender reputation.
SMTP vs IMAP vs POP3: Key Differences in Office 365
Understanding the difference between SMTP, IMAP, and POP3 helps you configure Microsoft 365 email correctly. Each protocol has a different role in email communication.
Protocol | Purpose | How It Works |
|---|---|---|
SMTP | Sending emails | Sends outgoing messages from your Microsoft 365 account, application, or device to the recipient's mail server. |
IMAP | Receiving and syncing emails | Keeps emails synchronized across multiple devices by storing messages on the mail server. |
POP3 | Downloading emails | Downloads emails from the server to a single device and may remove them from the server depending on settings. |
Which Protocol Should You Use?
For most Microsoft 365 users:
Use SMTP for sending emails through Outlook, applications, printers, and automated systems.
Use IMAP when you need email synchronization across multiple devices.
Use POP3 only when you need to download emails to a specific device.
For business applications and automated email sending, SMTP is the required protocol because it handles outgoing email delivery securely through Microsoft 365 servers.
Why Proper SMTP Configuration Matters
Email Deliverability is Everything
When your SMTP settings are correct, your emails reach people's inboxes. When they're not? Bounced messages, spam folders, and lost business opportunities. Proper configuration dramatically reduces delivery failures and keeps your communications reliable.
Security Can't Be Ignored
SMTP servers are prime targets for hackers. A solid Office 365 SMTP setup protects you through:
Better server authentication to stop unauthorized access
Up-to-date encryption for data protection
Strong password policies as an extra defense layer
One security breach could expose client information and damage your reputation that's why proper configuration is essential.
How to Set Up Office 365 SMTP Settings
Setting up Office 365 SMTP depends on where you want to send emails from. Microsoft 365 SMTP can be configured for email clients, business applications, printers, scanners, and other devices.
Before starting, make sure you have:
A valid Microsoft 365 email account
SMTP AUTH enabled if required
Port 587 available for outgoing connections
STARTTLS/TLS encryption supported by your application or device
Method 1: Configure Office 365 SMTP in Email Clients
To configure SMTP in an email client such as Outlook or another mail application, use these settings:
Outgoing SMTP Server: smtp.office365.com
Port: 587
Encryption: STARTTLS
Authentication: Required
Username: Your full Microsoft 365 email address
Password: Your Microsoft 365 password or app password (if MFA is enabled)
After entering the settings, send a test email to confirm the connection is working.
Method 2: Configure Office 365 SMTP for Applications
Many business tools such as CRMs, websites, monitoring systems, and automation platforms use SMTP to send emails.
Enter the following SMTP details:
SMTP Host: smtp.office365.com
SMTP Port: 587
Security: STARTTLS
Authentication: Enabled
Username: Microsoft 365 mailbox address
Password: Account password or app password
For applications that support modern authentication, Microsoft recommends using OAuth 2.0 instead of basic authentication.
Method 3: Configure Office 365 SMTP for Printers and Scanners
Printers and scanners often use SMTP for scan-to-email features.
Use:
Server: smtp.office365.com
Port: 587
Encryption: STARTTLS
Authentication: Required
If your device does not support TLS encryption or modern authentication, consider using an SMTP relay connector instead.
Method 4: Configure Office 365 SMTP Relay
SMTP Relay allows devices and applications to send email through Microsoft 365 without using a mailbox login.
SMTP Relay is commonly used for:
Printers
Copiers
Internal applications
Server notifications
To configure SMTP Relay:
Open the Microsoft 365 Exchange Admin Center.
Go to Mail Flow → Connectors.
Create a new connector.
Configure your trusted IP address or mail routing settings.
Test email delivery from your device or application.
SMTP Relay is different from authenticated SMTP because it relies on connector settings instead of mailbox credentials.
Common Issues and How to Fix Them
Even with a reliable platform like Office 365 SMTP, setup challenges can occasionally arise. Understanding these common issues and how to resolve them ensures uninterrupted, secure, and efficient email delivery.
Authentication Errors
Authentication errors are among the most frequent problems users encounter during SMTP configuration. They usually stem from incorrect login credentials, expired passwords, or disabled authentication settings.
How to Fix:
Double-check your username and password for accuracy.
Ensure SMTP authentication is enabled in your Office 365 account.
Activate multi-factor authentication (MFA) to enhance account security and reduce unauthorized access.
Port Configuration Problems
Port misconfiguration can prevent your emails from being sent successfully. Office 365 primarily uses Port 587 for secure transmission via TLS encryption. If this port is blocked by your firewall, emails may fail to deliver.
How to Fix
If issues persist, test with Port 25 as an alternative.
Verify that your SMTP settings are correctly aligned with Microsoft’s recommended configuration.
Connectivity Issues
Poor network connectivity or temporary server downtime can interrupt communication with the SMTP server, causing email delays or failures.
How to Fix:
Run a ping or traceroute test to check server accessibility.
Verify that your internet connection is stable.
Review server logs for detailed error messages to pinpoint the exact cause.
If problems continue, contact your network administrator or Microsoft support for advanced troubleshooting.
SMTP Authentication (SMTP AUTH) in Office 365 Explained
SMTP AUTH is the authentication method that allows applications, email clients, and devices to send emails through Microsoft 365 by signing in with a mailbox account.
When SMTP AUTH is enabled, the application connects to smtp.office365.com, provides the user's Microsoft 365 credentials, and sends email securely using SMTP submission.
Office 365 SMTP AUTH Requirements
Before using SMTP AUTH, check the following:
The mailbox must have SMTP AUTH enabled.
The application or device must support TLS encryption.
Port 587 should be used for secure email submission.
Multi-factor authentication (MFA) may require an app password or modern authentication support.
How to Enable SMTP AUTH in Office 365
To enable SMTP AUTH for a mailbox:
Open the Microsoft 365 Admin Center.
Go to Users → Active Users.
Select the mailbox you want to configure.
Open Mail settings.
Enable SMTP AUTH.
Save the changes and test the SMTP connection.
For organizations using Exchange Online, administrators can also manage SMTP AUTH settings through the Exchange Admin Center.
SMTP AUTH vs SMTP Relay vs Direct Send
Microsoft 365 provides different ways to send emails depending on your use case.
Feature | SMTP AUTH | SMTP Relay | Direct Send |
|---|---|---|---|
Requires mailbox login | Yes | No | No |
Uses SMTP authentication | Yes | No | No |
Requires connector setup | No | Yes | No |
Best for | Users, apps, email clients | Printers, devices, internal applications | Internal Microsoft 365 emails |
External email delivery | Yes | Yes | No |
SMTP AUTH
Best for:
Outlook and email clients
Business applications
Third-party tools
Automated email systems
SMTP AUTH uses a Microsoft 365 mailbox username and password to send messages.
SMTP Relay
Best for:
Printers
Scanners
Copiers
Internal business systems
SMTP Relay uses an Exchange Online connector and trusted IP addresses instead of mailbox credentials.
Direct Send
Direct Send allows devices and applications to send emails only to recipients inside your Microsoft 365 organization. It does not support sending messages to external email addresses.
Choosing the correct sending method depends on your device, application requirements, authentication support, and email delivery needs.
Best Practices for SMTP Management
Keep your Office 365 SMTP running smoothly with these habits
Regular Updates Keep settings current for security and efficiency
Security Protocols Use latest encryption methods and secure authentication
Monitor Logs Watch SMTP logs to catch issues early
Capacity Management Check storage and speed regularly to prevent overload
Verification Checks: Test settings periodically to ensure proper configuration
Security Tips for Office 365 SMTP
Protecting your email system should be a top priority
Always use TLS encryption for data in transit
Implement strong password policies across all accounts
Enable multi-factor authentication wherever possible
Regularly review and update connector settings
Monitor for suspicious activity in your logs
Limit SMTP relay permissions to only necessary users
Optimizing Email Performance
Get the most out of your Office 365 SMTP
Use dedicated connectors for different application types
Monitor delivery rates to identify potential issues early
Set up proper SPF and DKIM records to improve deliverability
Regular maintenance prevents small problems from becoming big ones
Keep documentation of your settings for troubleshooting
Wrapping It Up
Getting your Office 365 SMTP settings right goes beyond just sending emails it safeguards your business and preserves client relationships. Proper configuration ensures smooth operations and prevents costly email issues. With LiteMail's step-by-step guidance, you can confidently set up, troubleshoot, and maintain your email system. Now, managing your email workflow is simpler, more reliable, and fully under your control
Frequently Asked Questions About Office 365 SMTP Settings
What are the correct Office 365 SMTP settings?
The correct Office 365 SMTP settings are:
SMTP Server: smtp.office365.com
Port: 587
Encryption: STARTTLS
Authentication: Required
Username: Your full Microsoft 365 email address
These settings allow secure email sending through Microsoft 365 applications, email clients, and supported devices.
What is the SMTP server for Office 365?
The Office 365 SMTP server is smtp.office365.com. Microsoft recommends using this server with Port 587 and STARTTLS encryption for secure SMTP submission.
What port does Office 365 SMTP use?
Office 365 SMTP uses Port 587 with STARTTLS encryption. Port 587 is the recommended option because it provides secure email transmission and authentication.
How do I enable SMTP AUTH in Office 365?
To enable SMTP AUTH:
Open the Microsoft 365 Admin Center.
Select the required mailbox.
Open mail settings.
Enable authenticated SMTP.
Save changes and test the connection.
SMTP AUTH may also be controlled by organization-wide Exchange Online settings.
Why is my Office 365 SMTP not working?
Common reasons include:
Incorrect SMTP username or password
SMTP AUTH disabled
Wrong port or encryption settings
MFA requiring an app password
Device not supporting TLS encryption
Check that your configuration uses smtp.office365.com, Port 587, and STARTTLS.
Can I use Office 365 SMTP for bulk email sending?
Microsoft 365 SMTP has sending limits and is designed mainly for normal business communication, applications, and notifications.
For large cold email campaigns or high-volume outreach, a dedicated email infrastructure is usually more suitable.
What is the difference between SMTP AUTH and SMTP Relay in Office 365?
SMTP AUTH requires a mailbox username and password to send emails.
SMTP Relay uses Exchange Online connectors and trusted IP addresses, making it better for devices such as printers, scanners, and internal applications.
Can I use Office 365 SMTP with printers and scanners?
Yes, but the device must support SMTP authentication and TLS encryption.
For older printers or scanners that cannot support modern security requirements, Microsoft 365 SMTP Relay may be a better option.
Does Office 365 SMTP support Port 465?
No. Standard Office 365 SMTP submission uses Port 587 with STARTTLS encryption. Port 465 is not the recommended configuration for Microsoft 365 SMTP.
How can I improve Office 365 email deliverability?
To improve deliverability:
Configure SPF records
Enable DKIM signing
Publish DMARC policies
Maintain a good sender reputation
Monitor bounce rates and email activity
Final Thoughts
Setting up Office 365 SMTP correctly ensures your applications, email clients, and business devices can send messages securely and reliably. Using the correct configuration smtp.office365.com, Port 587, STARTTLS encryption, and proper authentication — helps prevent connection issues and improves email security.
For regular business communication, Microsoft 365 SMTP provides a reliable solution. However, organizations sending high-volume outreach or cold email campaigns should use dedicated email infrastructure designed for deliverability, inbox management, and sender reputation protection.
If you need Microsoft 365 mailboxes built for reliable sending with proper infrastructure, LiteMail provides pre-configured Microsoft 365 inboxes with setup support and deliverability-focused features.
