You may receive this error in your email client settings at some point. In Outlook this is a bug and can usually be resolved by restarting your email client and making sure you have SMTP authentication enabled.
This is not a server problem and is caused by a miconfigured email client, ISP's blocking access to port 25 and using port 26 instead or a DNS problem with your ISP.
To confirm that the mail server is online and responding you can perform the following:
From the 'Start' button click 'Run'
Type in telnet yourdomain.com 26
You should receive something to the effect of:
220-server.littleherohosting.com ESMTP Exim x.xx #1 day, xx Month 2008 time
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
This confirms there are *no problems* with the SMTP server
To confirm the POP server is online and responding:
From the 'Start' button click 'Run'
Type in telnet yourdomain.com 110
You should receive something to the effect of:
+OK POP3 [cppop x.x] at [xx.xx.xx.xx] (yourdomain.com)
This confirms the POP server is online and there are *no problems* with the POP server.
Link to Microsoft support: http://support.microsoft.com/default.aspx?scid=kb;en-us;q295164
Installing TELNET Client in Windows Vista
By default, Vista doesn�t install the Telnet client.
The client is for text-based communication with remote systems.
You can install it by following these steps:
1. Click Start then select Control Panel.
2. Select Programs and Features.
3. Select Turn Windows features on or off.
4. Select the Telnet Client option.
5. Click OK.
6. A dialog box will appear to confirm installation. The telnet command should now be available.
