I can receive mail but sending fails with "Sending reported error (0x80042109): Outlook is unable to connect to your outgoing (SMTP) e-mail server". This started after I changed my router. POP account on Outlook 2019.
Outlook error 0x80042109: cannot connect to outgoing SMTP server
Resolved
Email & Outlook
ZU
Zoe Underwood October 18, 2026
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That error means Outlook can not reach the SMTP server. After a router change the common causes are blocked ports or the wrong settings.
Check the outgoing server in File > Account Settings > More Settings > Advanced:
1. Outgoing server (SMTP) port 587 with encryption TLS, or port 465 with SSL. Port 25 is blocked by many providers.
2. On the Outgoing Server tab tick "My outgoing server (SMTP) requires authentication" and use the same settings as the incoming server.
3. Temporarily turn off any security suite that scans outgoing mail and test again.
Most providers also publish the exact SMTP host and port, so compare your settings with their help page.
Port was set to 25. Changed to 587 with TLS and mail sends now.
That was it. Many internet providers block port 25 on purpose, and a router reset can bring old defaults back.