A note should be added to -pra noting that the algorithm might have
unexpected results in rare cases where messages are formed according
to RFC822 rather than RFC2822:
Where messages conform to RFC822 rather than RFC2822, it is possible
for the algorithm to give unexpected results. An RFC822 message
should not normally contain more than one set of resent headers;
however the placement of those headers is not specified, nor are
they required to be contiguous. It is hence possible that the
Resent-From header will be selected even though a Resent-Sender
header is present. Such cases are expected to be rare or
non-existent in practice.
Implementations MUST use the algorithm as specified in this
document, even where the message is know to conform to RFC822.
-roy