Many internet service providers block the standard SMTP port 25 to reduce spam. This prevents Outlook from sending mail through your own email server. The solution is to configure Outlook to use an alternative SMTP port via a relay service. This article explains how to set up a mail relay and reconfigure your Outlook account.
Key Takeaways: Configuring SMTP Relay in Outlook
- File > Account Settings > Server Settings: Change the outgoing server port from 25 to 587 or 465 to bypass the ISP block.
- SMTP Authentication: Enable this setting and use your full email address as the username for the relay service.
- SSL/TLS Encryption: Select the correct encryption type required by your relay provider, which is often TLS on port 587.
Understanding SMTP Relay and Port Blocks
SMTP, or Simple Mail Transfer Protocol, is the standard for sending email. Port 25 is its default channel. Internet providers often block this port on residential connections to prevent compromised devices from sending spam directly. When blocked, your outgoing mail gets stuck in the Outbox.
An SMTP relay is a service that accepts your email on a different, open port and forwards it to the final recipient. Your email must be authenticated with the relay, proving you are not a spammer. You will need the server address, port number, and login credentials from a relay provider. Many email hosting companies offer this service.
Prerequisites for Configuration
Before changing Outlook, you must obtain SMTP relay credentials. This often comes from your email hosting provider, IT department, or a third-party service like SendGrid or Mailjet. You need the outgoing mail server hostname, the alternative port number, and your authentication username and password. The username is frequently your full email address.
Steps to Configure Your Outlook Account for Relay
Follow these steps to update your account settings. You must close and restart Outlook for changes to take full effect.
- Open Account Settings
In Outlook, go to File > Account Settings > Account Settings. Select your email account from the list and click Change. - Access Outgoing Server Settings
In the Change Account window, click More Settings. Then, navigate to the Outgoing Server tab. - Enable Authentication
Check the box for “My outgoing server requires authentication.” Select “Use same settings as my incoming mail server” or choose “Log on using” and enter the credentials provided by your relay service. - Change the Port Number
Go to the Advanced tab. In the Outgoing server field, change the port number from 25 to the one specified by your relay provider. Common alternatives are 587 for TLS or 465 for SSL. - Set Encryption Type
Below the port, use the dropdown to select the encryption method. For port 587, choose TLS. For port 465, choose SSL. Click OK. - Complete and Test
Click Next in the Change Account window. Outlook will test the account settings. If tests pass, click Close, then Finish. Restart Outlook and send a test email.
Common Mistakes and Configuration Errors
Outlook Test Fails on Outgoing Server
If the account test fails, verify your credentials. The username often needs to be your complete email address, not just the part before the @ symbol. Confirm the exact server hostname and port with your relay provider. Ensure your password is correct and does not contain special characters that need escaping.
Emails Stay in Outbox After Configuration
This usually means the connection is still being blocked. Temporarily disable Windows Defender Firewall and any third-party antivirus software to test. If mail sends, you must add an exception in your security software for Outlook. Also, confirm your ISP is not blocking the new port you selected.
Relay Service Rejects Authentication
Some services require you to enable SMTP authentication in your hosting control panel first. Log into your email provider’s web portal and check for an “SMTP Relay” or “External Mail Client” setting that must be activated before Outlook can connect.
Direct Send vs Authenticated Relay: Key Differences
| Item | Direct Send (Port 25) | Authenticated Relay (Port 587/465) |
|---|---|---|
| Primary Port | 25 | 587 or 465 |
| ISP Blocking | Often blocked on residential networks | Rarely blocked, designed for mail clients |
| Authentication | Not typically required | Always required with username/password |
| Encryption | Usually none | SSL or TLS encryption is standard |
| Best Use Case | Server-to-server communication | Sending from email clients like Outlook |
You can now send email from Outlook even with a port 25 block. Use the correct relay port and encryption settings provided by your email host. For advanced control, investigate setting up a local SMTP relay server on a business network. Always test your configuration with a message to yourself first.