Request for Root Cause of Email outage

Looks like everyone lost ability to send email out to Gmail, Hotmail, etc.  for several days or until they notice it.   This shakes our confidence in using this email service.  

Could you please post an analysis of what went wrong  and why, and what you or we could or should have done to avoid it.  Was it an IP address change on your end? Was there any announcement?  People are still posting the problem a week later.

Support (Mike & Todd) have been swift in providing good answers to queries (Thank you guys) but why is this dumped on them.   I need an official explanation from company management to have confidence it won't happen again.  My business depends on reliable email.

Thx

- Andrew