Mail set up / Can't send Please help....

Hi,
I am a new iMac user. Pretty experienced PC user. I am having problem setting up mail - It should be pretty simple but it hasn't been...

I am on the (UK) Orange network, but currently download my work (POP) mail onto my PC into Outlook from my business.com server.
I also have a Onetel account that I do the same. Download my personal messages into Outlook. All has been working very smoothy and I am sure of all passwords.

I can Receive mail through the Mac Mail programme. But I cannot send.
I have tried all combinations of passwords and usernames. When I send, I just get the little spinning wheel going round and round for hours....

in Mail, I have set up an account for each of my email accounts/addresses. Sometimes 1 or more will say Offline - Why ?? I have not done anything to cause this. What caused it to go offline? I am still connected and do have access to the Web.
I get a message from time to time that says "Cannot send message using the server (null)" Is this pertaining to the Orange Broadband server I have my router connected to? I have no home server.
I have used all the same settings from my PC for these accounts but just cannot get it working. Does Mac use different settings ?

I did a search online and found a site that said if using a pop account to use port 587 instead of 25 - tried this, had no effect.

Does anyone know Exactly what you are to add to each box?

Please help. Everyone said using an Apple is so easy....

ppthepom

 

Sorry ~ This was the first post I have ever done on this site and it didn't seem to have gone though... But obviously it did.

I'll be more careful in the future...