Mail on 10.3.5 keeps going to Offline Mode

I am using OS X on my Mac. Recently, the Mail on 10.3.5 keeps going to offline mode.
When I switch it back to online, it will go offline again when trying to open my emails.
The settings for this are set correctly and yet I was still unable to fix it.
It cannot even hook up to mail or DNS servers.
How will I fix it?
Let me know please.
