First, make sure you have checked in the account properties of the Outlook Express / MS Outlook the option “My server requires authentication”. Please note that if you are using a different email client the settings might be different.
If not, proceed to the following test. Open Command Prompt (Windows -> Start menu -> Run -> type “cmd”) and type:
For clients with premium hosting accounts:
telnet mboxhosting.com 25
For free hosting clients:
telnet free.mboxhosting.com 25
If you do not get a response 220 mboxhosting.com mail server or 220 free.mboxhosting.com mail server this means your PC (Firewall or Antivirus Program) blocks port 25 and thus filters your outgoing emails.
Solution: Disable the option of your/your network firewall to block port 25, contact system administrator, ISP, or Antivirus Program producer for help on how to disable port 25 filterings. Alternatively, you may use port 587.