I've assigned Issue 17 to the question of whether, if reply
lines constitute a continuation set, all of the codes are
expected to be the same and whether this needs clarification.
It appears that there are three options:
(i) Do nothing, leaving the text as is
(ii) Make it clear that the codes may be different and
that clients are expected to examine all of them.
(iii) Prohibit different codes and, optionally, suggest
that it is ok for a client to select one of them and
assume that all of the others are the same.
If we select (ii), we may need to make a statement about which
of the codes is the "final" one with regard to client actions,
especially if the first digits are different.
Note that this may (or may not) have an impact on various
proposals for delayed responses to RCPT, so any new text that
goes in may need explicit provisions for extensions changing the