Microsoft live to Sky email failure

[blackscooby]

Not directly affecting myself, but it is affecting our Motor Club. We have committee members who have .live.co.uk (Microsoft) email addresses who cannot send to sky.com email addresses.

I'm not affected as I use neither Sky or Microsoft for my mail provider.

Final-Recipient: rfc822;<username>@sky.com
Action: failed
Status: 5.4.300
Diagnostic-Code: smtp;550 5.4.300 Message expired -> 421 4.4.2 Connection dropped due to SocketError

I can send and receive to both the .live.co.uk and the .sky.com members.

Anyone know if there is anything that can be done at a user end to address this ?

Thanks
BS