Hi,
As a long time implementer and integrator of IETF protocols, my mail
engineering view ….
The thing is RFC 822, 2822 and 5322 allows for a single 5322.From header to
have multiple addresses:
from = "From:" mailbox-list CRLF
mailbox-list = (mailbox *("," mailbox)) / obs-mbox-list
So it is
I have a data point.
When we (Google) did an experiment/analysis of this a couple of years ago
the conclusion was
a) multi-value From are relatively rare and mostly look like abuse or
mistakes rather than intentional.
b) Users generally don't care about those messages if they end up in spam.
