Greylisting
Email sent to cs.uchicago.edu addresses is greylisted, in an attempt to reduce the amount of spam.Our email server temporarily blocks any email from a sender it does not recognize. The sending email server, if following email protocols correctly, will resend the message after some period of time. Greylisting is effective because many mass email tools used by spammers will not bother to retry a failed delivery, so the spam is never delivered.
The downside of greylisting is that email may be delayed. The delay cannot be predicted, as it depends on the configuration of the sending email server, though 15 minutes is typical.
All CS email accounts are greylisted by default, but you can opt-out: just let us know at techstaff@cs.uchicago.edu. You may also request to have a sender's address whitelisted, so it will not be subject to our greylisting system. Email that is blocked by our greylisting service and not re-sent by the sender cannot be recovered.
Note, greylisting is independent of our email tagging and filtering system.