420:Socket error from Virginmedia SMTP

Hello,

I have previously received emails from this particular sender and then this weekend he said to me, your emails are being rejected.  He is on virginmedia in the uk.

He has subsequently sent me the failure message to my work email:

    Subject: Delivery Status Notification

    This is the mail system at host know-smtprelay-4-imp.

    I am sorry to have to inform you that your message, "Your address...", could not be delivered to recipient@mydomain.co.uk.

    The remote mail system said;

    420:Socket error

    The original message is attached.

I have a feeling this is to do with the virgin media smtp servers are trying to use The SSL or TLS protocols that have been disabled in v.17

Nothing is being shown up in the email logs to even suggest a connection has been attempted.

Current XG version: 17.0 GA

Mail settings: MTA Mode

Any help would be greatly appreciated.

Thanks

Ian