The protocol specified in this document may be satisfactory for
limited use in private wireless IP networks. However, it is
unsuitable for general-purpose message transfer or for transfer of
messages over the public Internet, because of limitations that
include the following:
- Lack of congestion control
EMSD is layered on ESRO [RFC 2188], which does not provide
congestion control. This makes EMSD completely unsuitable for
end-to-end use across the public Internet. EMSD should be
considered for use in a wireless network only if all EMSD email
exchanged between the wireless network and the public Internet
will transit an EMSD<->SMTP gateway between the two regions.
- Inadequate security
The document specifies only clear-text passwords for
authentication. EMSD should be used across a wireless network
only if sufficiently strong encryption is in use to protect the
clear-text password.
- Lack of character set internationalization
EMSD has no provision for representation of characters outside of
the ASCII repertoire or for language tags.
- Poorly defined gatewaying to and from Internet Mail
Because Internet Mail and EMSD have somewhat different and
conflicting service models and different data models, mapping
between them may provide good service only in limited cases, and
this may cause operational problems.
The IESG therefore recommends that EMSD deployment be limited to
narrow circumstances, i.e., only to communicate with devices that
have inherent limitations on the length and format of a message (no
more than a few hundred bytes of ASCII text), using either:
a. wireless links with adequate link-layer encryption and gatewayed
to the public Internet, or
b. a private IP network that is either very over-provisioned or has
some means of congestion control.
In the near future, the IESG may charter a working group to define an
Internet standards-track protocol for efficient transmission of
electronic mail messages, which will be highly compatible with
existing Internet mail protocols, and which wil be suitable for
operation over the global Internet, including both wireless and wired
links.