Post Office Protocol: Version 2

Simple Mail Transfer Protocol

“…In some cases, the domain name(s) transferred to, or determined by, an SMTP client will identify the final destination(s) of the mail message. In other cases, common with SMTP clients associated with implementations of the POP [3,26] or IMAP [6] protocols, or when the SMTP client is inside an isolated transport service environment, the domain name determined will identify an intermediate destination through which all mail messages are to be relayed. SMTP clients that transfer all traffic, regardless of the target domain names associated with the individual messages, or that do not maintain queues for retrying message transmissions that initially cannot be completed, may otherwise conform to this specification but are not considered fully-capable.…”

“…The problems associated with ill-formed messages were exacerbated by the introduction of the split-UA mail reading protocols [3,26,5,21]. These protocols have encouraged the use of SMTP as a posting protocol, and SMTP servers as relay systems for these client hosts (which are often only intermittently connected to the Internet).…”

Post Office Protocol: Version 3: Extended service offerings

“…As discussed in [RFC1081], the problem of giving workstations dynamic access to mail from a mailbox server has been explored in great detail (originally there was [RFC918], this prompted the author to write [RFC1081], independently of this [RFC918] was upgraded to [RFC937]). A natural solution to the problem outlined above is to keep discussion group mail on a mailbox server at each site and permit different hosts at that site to employ the POP3 to access discussion group mail.…”

Evaluation of a DTN convergence layer for the AX.25 network protocol

“…A DTN Convergence Layer for the AX.25 protocol was developed to allow AX.25 nodes to partake in DTN transfers. Tools [9] already exist to use a DTN network for the transport of email that present a standard SMTP [13] and POP [4] interface to a user's existing email application.…”