I don't know which concerns me more; the fact that it went wrong or the fact that Sky haven't acknowledged that it went wrong.
Seems not uncommon for Sky.
For instance the thread below proves the Sky SMTP server has been failing to deliver messages with no notification to either party. Whilst the issue has since been fixed after Sky reported it to Yahoo, we've heard no official confirmation from Yahoo about anything.
Given how busy the Sky SMTP server is, this could have resulted in a huge amount of lost mail.