Some transports restrict the use of characters with ordinal values greater than 127 (decimal). Most notably, some SMTP servers will strip the high bit and thus garble messages that use characters in this "eight bit" range.g
PMDF provides facilities to automatically encode such messages so that
troublesome eight bit characters do not appear directly in the message.
This encoding can be applied to all messages on a given channel by
sevenbit keyword. A channel should be
eightbit if no such restriction exists.
Some transports such as extended SMTP may actually support a form of
negotiation to determine if eight bit characters can be transmitted.
eightnegotiate keyword can be used to instruct the
channel to encode messages when negotiation fails. This is the default
for all channels; channels that do not support negotiation will simply
assume that the transport is capable of handling eight bit data.
eightstrict keyword tells PMDF to reject any messages
that contain unnegotiated eight bit data.
g Indeed, there have even been reports of SMTP servers which will crash when presented with eight bit data.