The Internet Message Transfer Agent (IMTA) routes, transports, and delivers Internet Mail (RFC 822) messages within the email system.The IMTA performs all of its operations on a set of channels. There are two types of channels: internal and external. An internal channel is an interface between internal modules of the IMTA. Internal channels include the reprocessing, conversion, and defragmentation channels. These channels are not configurable from the SIMS Administration Console.
An external channel is an interface between the IMTA and another SIMS component (i.e., the Sun Message Store), or another component outside of SIMS (for example, the Internet or a local mail client). The external channels are configurable.
Post Office Protocol Version 3 (POP3) is an implementation of the server side of the POP3 (RFC 1939) access protocol standard. Many popular mail clients currently use POP3.Internet Mail Access Protocol Version 4 is an implementation of the server side of the standard IMAP4 protocol (RFC 2060). IMAP4 is used by client mail applications to access Internet email messages in distributed, enterprise/Internet-wide message stores.
Note - With /var/mail enabled, the server supports only IMAP4. Clients which require IMAP4rev1 cannot be used. With /var/mail disabled (which is the default), the server supports both IMAP4 revision 1 and IMAP4 access protocols.