Outlook SMTP Configuration
Use these exact values when configuring any email client or application to send through Outlook's servers.
| Parameter | Outlook.com | Microsoft 365 |
|---|---|---|
| SMTP Host | smtp-mail.outlook.com |
smtp.office365.com |
| SMTP Port | 587 |
587 |
| Encryption | STARTTLS | STARTTLS |
| Username | Your full Outlook email | Your Microsoft 365 email |
| Authentication | Modern Authentication or password | OAuth2 or password |
Note: Microsoft recommends using OAuth2 for authentication when possible. If your application does not support OAuth2, use your Microsoft account password with Modern Authentication enabled on your account.
Step-by-Step Setup
Follow these steps to configure SMTP access for your Outlook or Microsoft 365 account.
1. Enable Modern Authentication
Navigate to your Microsoft account security settings and enable Modern Authentication. This is required for SMTP access on most Microsoft 365 accounts.
2. Allow IMAP/SMTP Access
In your Outlook settings, ensure IMAP and SMTP are enabled under "Mail" → "Sync email" → "POP and IMAP settings."
3. Configure Your Application
Enter smtp-mail.outlook.com as the SMTP host, port 587 with TLS enabled, your full Outlook email as the username, and your password as the credential.
4. Send a Test Message
Verify the configuration by sending an email to yourself. Check your sent folder in Outlook web to confirm delivery.
Common Errors and Solutions
Most Outlook SMTP issues fall into a handful of categories. Here's how to fix them quickly.
Authentication Failed
If using basic authentication, ensure your account password is correct. For Microsoft 365 accounts, verify that Modern Authentication is enabled and that your admin has not blocked SMTP authentication.
Connection Timeout
Port 587 may be blocked on restrictive networks. Try port 25 with TLS as an alternative. If that fails, the network firewall may be blocking outbound SMTP entirely.
5.7.57 Client Does Not Have Permissions
This error occurs when the admin has disabled SMTP AUTH on your Microsoft 365 tenant. Contact your Office 365 administrator to enable SMTP AUTH for your account.
Tenant Has Exceeded Threshold
Microsoft 365 has tenant-wide sending limits. If you are sending high volumes, consider using a dedicated email service with proper infrastructure to avoid throttling.
Best Practices for Outlook SMTP
Keep your account secure and your messages deliverable with these recommended approaches.
Use OAuth2 When Available
OAuth2 authentication is more secure and does not require storing your actual password. It also avoids issues with app passwords expiring.
Monitor Account Security
Review your Microsoft account's recent activity regularly. Unusual login attempts may indicate your credentials are compromised.
Avoid High-Volume Sending
Outlook and Microsoft 365 have strict rate limits. For transactional email or marketing campaigns exceeding 100 emails per day, use a dedicated SMTP relay service.
Set Up SPF Record
If sending from custom domains through Outlook, add the appropriate SPF record to your domain's DNS to prevent your messages from being flagged as forged.
When Outlook SMTP Falls Short
Outlook's SMTP service is suitable for low to moderate volume sending, but production applications quickly encounter rate limits and lack of deliverability analytics. A dedicated email API gives you webhooks, detailed logs, and infrastructure built for deliverability at scale.
For teams sending across multiple domains or needing intelligent routing rules, a SMTP relay service prevents your messages from being flagged as suspicious. Learn more about improving email deliverability through correct authentication setup.
For cold outreach or new sender addresses, an email warmup strategy gradually builds your sender reputation instead of triggering spam flags with sudden high-volume bursts.
Frequently Asked Questions
What is the difference between Outlook.com and Microsoft 365 SMTP?
Outlook.com uses smtp-mail.outlook.com and is for personal Microsoft accounts. Microsoft 365 uses smtp.office365.com and is for business accounts with an Office 365 subscription. Both use the same port and encryption settings but have different authentication requirements.
Why is SMTP AUTH disabled on my Microsoft 365 account?
Your organization's Office 365 admin may have disabled SMTP AUTH for security reasons. In this case, you need to contact your admin to enable it, or use OAuth2 authentication which is more secure and often allowed even when basic AUTH is disabled.
Do I need 2FA for Outlook SMTP?
If your Microsoft account has multi-factor authentication (MFA) enabled, you will need to use an App Password instead of your regular password for SMTP authentication. Microsoft recommends enabling MFA for all accounts.
What are Microsoft 365 SMTP sending limits?
Microsoft 365 has different limits depending on your plan. Standard plans typically allow 30,000 emails per day per mailbox, with a maximum of 10 recipients per message. Shared mailboxes have lower limits. For higher volume, use a dedicated email service.
Can I use Outlook SMTP for automated emails?
Outlook SMTP is not designed for high-volume automated emails. If you need to send transactional emails or automated notifications at scale, consider using a dedicated email API service that provides proper infrastructure, webhooks, and analytics.
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