where can I find my IMAP Path Prefix for MAIL?

I am unable to send mail from my IMAC OS X v 10.6.8. I use Airport Extreme and Use a WiFi Network. This only happened recently but whenever I try to sent a message it says “Can’t send message using the server smpt.aol.com" This is what I use and if I hit connection doctor both aol mail and smtp.aol.com are both green and says able to connect to the interenet. So what is the problem with my Apple Mail or what am I doing wrong. I also tried setting on mail on my IPOD Version 6.1.6. I am unsure what is causing this. Any help will be greatly appreciated. Would this have anything to do with Icloud. I have Icloud mail but right now it’s shut off on my ipod.