requirement
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... client and server to agree to
utilize shared functionality beyond the original SMTP requirements.
The SMTP extension mechanism defines a means whereby an extended SMTP ...
... MUST - This word, or the terms "REQUIRED" or "SHALL", mean that
the definition is an absolute requirement of the specification.
...
... accepted if the client tries again later). Despite the apparent
scope of this requirement, there are circumstances in which the
acceptability of the reverse-path may not be determined until one or
more forward-paths (in RCPT commands) can be examined. In those
...
... POP3 or IMAP, that have limited
capability to support some of the requirements of this specification,
such as the ability to queue messages for subsequent delivery ...
... Gatewaying mail between different mail environments, such as
different mail formats and protocols, is complex and does not easily
yield to standardization. However, some general requirements may be
given for a gateway between the Internet ...
... header fields of a message that it
forwards into the Internet mail environment meet the requirements for
Internet mail. In particular, all addresses ...
... necessary if the server always returns 554 on connection opening (as
described in section 3.1). The requirement to accept mail for
postmaster implies that RCPT commands which specify a mailbox for
...
... host can now be sent.
Application of this principle may, in many cases, eliminate the
requirement for an explicit "send queues now" function such as ETRN
...
... routing to get mail
from one host to another via a series of relays. The requirement to
utilize source routes in regular mail traffic ...
... significant justification for them was eliminated by the
introduction, in RFC 1123std3, of a clear requirement that addresses
following an "@" must all be fully-qualified ...