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.
Messaging Server 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 enqueued to a given channel by specifying the sevenbit keyword. A channel should be marked eightbit if no such restriction exists.
The SMTP protocol disallows eightbit “unless the remote SMTP server explicitly says it supports the SMTP extension allowing eightbit.” Some transports such as extended SMTP may actually support a form of negotiation to determine if eight bit characters can be transmitted. Therefore, the use of the eightnegotiate keyword is strongly recommended 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.