If you receive the following error in your Outlook application:

this means that your application fails to connect to the SMTP server you have set for your e-mail account.

Most commonly such issues occur when the port for your SMTP connection is filtered by a local firewall application or by your Internet service provider.

Therefore, you can try changing the port you use to connect to the SMTP server from 25 to 2525. If this doesn't help, you can try disabling or re-configuring your firewall and anti-virus applications you have installed on your computer.

If none of the above works and you continue to receive this error, you should contact your Internet service provider. They should be able to provide you with more detailed information on whether they are filtering any ports used for SMTP connections.