Getting my imap account to work

i have a domain and i want to get my IMAP account to work. but i cant seam to do this in mac mail. the pop account works great but i have 3 different places i read it from. (iMac, MBP & iPhone) when ever i put in the setting for IMAP i just take the account off line.

I used the terminal command
$ telnet imap.1and1.com 143

and i get a message telling me that the server is working but i cant get into via the mail program