Email messages addressed to Yahoo domains (yahoo.com, yahoo.ca, etc.) from McGill mail servers are currently being delayed. It seems the Yahoo server has "greylisted" McGill email, probably due to a large quantity of emails coming from McGill within a short period of time.
Mail is delivered eventually, but the delays can be anywhere from 15 minutes to 4 hours, depending on which the yahoo destination server is the recipient.
We apologize for any inconvenience this causes and thank you for your patience.