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I was installing a new intranet with new domain and webmail only for inside my company.<br />
I did <br />
telnet localhost imap<br />
receive ok<br />
01 login username userpassword<br />
receive <br />
01 NO login Fauled<br />
<br />
courier and postfix are running
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I was installing a new intranet with new domain and webmail only for inside my company.
I did 
telnet localhost imap
receive ok
01 login username userpassword
receive 
01 NO login Fauled

courier and postfix are running

telnet localhost imap error

Interactions between email servers and clients are governed by email protocols. The three most common email protocols are POP, IMAP and MAPI. Most email software operates under one of these (and many products support more than one).  The correct protocol must be selected, and correctly configured, if you want your email account to work.

Email Protocols

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.