BleepingComputer.com: Email message "could not send message for past 4 hours" need help

At work we are having problems receiving an email with an encrypted attachment from another company. Monthly they send alerts to do with debit cards and since they have been doing this everytime we never get the email and they eventually get mail delivery subsystem error back saying " could not send message for past four hours {encrypt On Reply}" in the body of the email it says "timeout writing message to (name of my email server) : resource temporarily unavailable ( the email address it is trying to be sent to)" I have check on our end the smtp log file and it never even shows the email hitting our gateway so I dont see why we would be blocking the email. It seems to me this is something on thier end but they cant find a solution. Once again this is an email with an encrypted attachment that is an alert.. it is emailed to a distribution email address then sent to evryone in that distribution list. They get other emails fine it is just this certain one that we cant get. Does anyone have any idea what could be keeping this email from coming through?