We have been having problems receiving email from another company that has recently started using Microsoft exchange digital signature. I have tried white-listing the the companies email addresses "*@company.com" but have had no luck. This is the message they receive when they try to send an email to us:
"Delivery has failed to these recipients or distribution lists:
Your message wasn't delivered because of security policies. Microsoft Exchange will not try to redeliver this message for you. Please provide the following diagnostic text to your system administrator."
All help would be appreciated!