About 90% of SMTP is spam. SMTP from Tor nodes is so close to 100%
that I don't know anyone who accepts mail from them.
Um, 90% by weight or by volume?
About the same either way.
More seriously what's the claim there: number of connections? Bytes?
Messages? Recipients? (A possibility is that all of them are 90%, but
that seems unlikely to me and would be worh pointing out, too.)
Really, it's about the same. People have been collecting stats on this
for upwards of a decade. For more details, Google is your friend.
Besides which 90% vs 100% doesn't seem very significant to me.
I gather you've never run a large mail system or talked to people who do.
The 90% is an average over all sources. Some sources like the IETF's mail
system send about 0% spam, some like Tor and botnetted old Wordpress
servers send 100%, others are in between. To keep the load manageable,
you reject mail from the very spammy sources and use your servers to
filter what you accept.
There's a reason that every mail system of any size has a Spamhaus
subscription.
R's,
John