Things to Know

All e-mail sent to users on any domain hosted by Operation Email
is checked against the following Open Relay List(s):

dnsbl.njabl.org

opm.blitzed.org

This is done to protect against SPAMMERS sending messages to user accounts hosted by Operation Email. If a company/individual  is unable to send you an e-mail because of this, they need to fix their mail servers and prevent it from being an "open relay" for SPAMMERS.