Microsoft 365 SMTP Configuration
Use these exact values when configuring any email client or application to send through Microsoft 365 servers.
| Parameter | Value |
|---|---|
| SMTP Host | smtp.office365.com |
| SMTP Port | 587 (TLS/STARTTLS) |
| Encryption | STARTTLS on port 587 (required) |
| Username | Your full Microsoft 365 email address |
| Password | Your Microsoft 365 password or App Password (if MFA is enabled) |
Important: If your Microsoft 365 account has Multi-Factor Authentication (MFA) enabled, you must generate an App Password. Regular passwords will fail for SMTP when MFA is active.
Step-by-Step Setup
Follow these steps in order to configure SMTP access for your Microsoft 365 account.
1. Check SMTP Settings in Exchange
In the Microsoft 365 admin center, go to Exchange Admin > Mail flow > connectors. Ensure the "Allow users to submit mail to MIMEcast" setting is enabled if applicable to your organization.
2. Handle MFA if Enabled
If your account uses MFA, sign in to your Microsoft account and generate an App Password under Security Info. Use this password for SMTP instead of your regular account password.
3. Configure Your Application
Enter smtp.office365.com as the SMTP host, port 587 with TLS enabled, your full Microsoft 365 email as the username, and your password or App Password as the credential.
4. Send a Test Message
Send an email to yourself and an external address to confirm delivery. Check your Microsoft 365 sent folder to verify the message was sent successfully.
Common Errors and Solutions
Most Microsoft 365 SMTP issues fall into a handful of categories. Here's how to fix them quickly.
Authentication Failed
If MFA is enabled, you need an App Password. Generate one at myaccount.microsoft.com under Security Info. If MFA is off, verify your regular password is correct and that the account isn't locked.
SMTP Disabled by Admin
Microsoft 365 admins can disable SMTP client submission in the Exchange admin center. If you get an "SMTP not enabled" error, contact your IT administrator to enable it.
Connection Timeout
Port 587 is required for Microsoft 365 SMTP. Port 465 is not supported. If port 587 is blocked by your network, use a different network or VPN to connect.
Send Limit Reached
Microsoft 365 has per-mailbox sending limits (typically 10,000-30,000 per day for licensed accounts). For production applications exceeding these limits, use a dedicated email service.
Best Practices for Microsoft 365 SMTP
Keep your account secure and your messages deliverable with these recommended approaches.
Use App Passwords with MFA
When MFA is enabled on Microsoft 365, always use App Passwords for SMTP. Generate unique App Passwords per application for easier revocation.
Enable Modern Authentication
Modern Authentication (OAuth 2.0) provides better security than basic password authentication. Enable it in the Microsoft 365 admin center and update your applications to use OAuth where possible.
Configure SPF and DKIM
Enable DKIM signing in the Microsoft 365 admin center and add the appropriate SPF record to your domain's DNS to improve deliverability and prevent spoofing.
Use Shared Mailboxes for High Volume
For automated applications, consider using a shared mailbox rather than a user account. Shared mailboxes don't consume user licenses and can reduce the risk of individual account lockouts disrupting sending.
When Microsoft 365 SMTP Falls Short
Microsoft 365's SMTP service works well for standard business email needs, but production applications with high-frequency transactional sending quickly encounter rate limits and operational constraints. Microsoft provides no webhook notifications for delivery events, limited bounce handling, and no granular analytics. A dedicated email API provides the infrastructure and observability that production transactional email requires.
For teams needing reliable transactional email at scale, SMTP relay services handle authentication, IP reputation, and routing automatically. Learn more about email deliverability and why sender reputation matters for inbox placement.
Frequently Asked Questions
What are Microsoft 365's SMTP sending limits?
Microsoft 365 mailboxes are typically limited to 10,000 external recipients per day and 30,000 total messages per day depending on the license. Enterprise plans may have higher limits. For volume above these limits, use a dedicated email service.
Can I use SMTP with a shared mailbox in Microsoft 365?
Yes. Shared mailboxes can send via SMTP using their email address and credentials. However, they require a licensed user account to be set as the owner for authentication purposes.
Is port 465 supported for Microsoft 365 SMTP?
No. Microsoft 365 only supports SMTP on port 587 with STARTTLS. Port 465 is not supported. Ensure your application uses port 587 for Microsoft 365 SMTP connections.
My Microsoft 365 SMTP is being rejected. What should I do?
Verify SMTP client submission is enabled in Exchange Admin Center. Check if MFA requires an App Password. Ensure your password is correct and the account isn't locked. Try using a different network to rule out firewall issues.
Can I send from multiple domains with Microsoft 365 SMTP?
Yes, if your Microsoft 365 tenant is configured for multiple domains, you can send from any domain added to your tenant. The sending identity must be a valid mailbox or group in your organization.
Ready to move to reliable email infrastructure?
Start free with no card, or talk to sales for high-volume and enterprise.
Start SendingTalk to Sales