At approximately 11AM EST, one of the ExchangeDefender outbound network endpoints (outbound3.exchangedefender.com) was brought into rotation without all the relay ACLs authorized. The result is the message below for some clients/domains whose policies did not load properly. The error they received is a 500 Relaying Denied, and it's been fixed/addressed.
Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept e-mail from certain senders, or another restriction may be preventing delivery.
The following organization rejected your message: outbound3.exchangedefender.com.
If you received this error message, please go to your Sent Items and resend the message.