Update 01/24/2020 17:41 PM 17 hrs
We are currently working with British Telecom to address an issue on their servers related to their implementation of synchronoss.net software. What our customers are experiencing, intermittently, are delivery delays while sending messages to btinternet and associated properties. The issue was first reported to us around 9AM EST and was quickly addressed to bypass/mask the ExchangeDefender network and route around the problem until BT has a chance to figure out why their DNS and outsourced mail service are having issues with DNS resolution.
Current error produced on their side is:
421 re-prd-rgin-021.btmx-prd.synchronoss.net Service not available - no PTR record for x.x.x.x
As of 10:15 AM this morning this issue has been addressed for our customers so they can send mail to BT, however, this is an issue outside of ExchangeDefender's control and free/ISP mail staff tend not to be very concerned about email delivery issues in general so we do not expect a quick resolution nor can we estimate an ETA.