To connect a third-party email client, CRM, or application to an Outlook or Microsoft 365 account, you need the correct SMTP (outgoing mail) settings. A wrong port or missing authentication setting is one of the most common reasons Outlook mail bounces or fails silently — often without a clear error message. Here's exactly what to enter.
Outlook SMTP Settings at a Glance
| Setting | Value |
|---|---|
| SMTP server | smtp-mail.outlook.com |
| Port (recommended) | 587 (STARTTLS) |
| Alternative port | 465 (SSL/TLS) |
| Username | Your full Outlook email address |
| Password | Your Outlook account password (or app password, if required) |
| Authentication | Required |
How to Configure SMTP in Outlook
- Open Outlook and go to File > Account Settings > Account Settings.
- Select the email account you want to configure and click Change.
- Scroll to the "Outgoing mail server (SMTP)" field and enter the server address and port from the table above.
- Make sure "My outgoing server (SMTP) requires authentication" is checked.
- Choose the correct encryption method (STARTTLS or SSL/TLS) to match your chosen port.
- Click Next, then use "Test Account Settings" to confirm Outlook can send a test message successfully.
Outlook IMAP Settings
IMAP keeps your mailbox synced across devices in real time — a message read or filed on one device shows the same status everywhere.
- Server: imap-mail.outlook.com (or check your account's specific server if using Microsoft 365)
- Port: 993
- Encryption: SSL/TLS required
Outlook POP3 Settings
POP3 downloads mail to a single device, which suits offline, single-computer use better than multi-device access.
- Server: pop-mail.outlook.com
- Port: 995 (SSL) — port 110 is used only for unencrypted connections, which is not recommended
- Encryption: SSL enabled
Sending Limits
- Free Outlook.com accounts: roughly 300 recipients per day, with a maximum of 100 recipients per message.
- Microsoft 365 / Exchange Online accounts: 10,000 recipients per day per user, with a per-message cap of 500 recipients (an admin can raise this to 1,000).
Troubleshooting Common Issues
Authentication error
Double-check your username and password for typos, and confirm your account's security settings (like SSL/TLS requirements) match what your client is using.
Server not found
Verify the server address is typed exactly as shown above, and confirm your internet connection is stable — this error also sometimes points to a temporary outage on Microsoft's side.
Connection fails specifically on SMTP (outgoing) but IMAP works fine
Recheck your outgoing port and encryption setting — a mismatch here is common even when incoming mail is configured correctly. You can also enable troubleshooting logging in Outlook (File > Options > Advanced > Other) to see exactly where the connection fails.
Frequently Asked Questions
Which port should I use for Outlook SMTP?
Port 587 with STARTTLS is the recommended default; port 465 with SSL/TLS is a supported alternative.
How often should I update my Outlook password for security?
Changing it every three to six months is a reasonable baseline, along with updating your SMTP settings anywhere they're stored if you do change it.
Why does authentication keep failing even with the correct password?
Make sure "outgoing server requires authentication" is checked in your client — Outlook's SMTP server won't accept unauthenticated connections.
