It appears that the University of Washington blocking Riseup emails as spam. And, no, I'm not sending spam.
Here are the recent error messages I'm getting:
: host mxe25.s.uw.edu[188.8.131.52] said: 550 5.7.1 184.108.40.206 explicitly prohibited from sending mail for this domain by sender's published policy (in reply to end of DATA command)
: host mxe24.s.uw.edu[220.127.116.11] said: 550 5.7.1 Message not accepted as it appears to be spam (in reply to end of DATA command)
It appears Riseup has been blacklisted by by sorbs.net. See .