Update 29 May

General update

All mail.coop systems are running correctly

Outlook.com and Hotmail ‘Rate limit’

This has now been cleared

Microsoft systems removed the rate limit imposed on incoming mail.coop at approximately 7pm on 24 May.


In our post of 24 May we referred to the ‘rate limit’ imposed on incoming traffic from mail.coop users by Microsoft (which operates Outlook.com and Hotmail) services.

  • Users sending to Outlook.com and Hotmail addresses would receive a bounce message saying that their message would be delayed, but that it was not necessary to re-send. An experimental email sent on 24 May was delayed 2 hours.
  • The bounce message referred to a rate limit imposed because of ‘ip reputation’.
  • In response to our enquiries, Microsoft said “Nothing was detected to prevent your mail from reaching Outlook.com customers.” Nevertheless several users reported the bounce messages.
  • Our tech team commented: “Analysis of messages is machine learning driven at Hotmail/Outlook (with 100 millions of users it is not possible for these to managed otherwise). A new IP sending email will have a poor reputation by default. This applies to a new service like mail.coop and will improve over time.”
  • This was borne out by the removal of the rate limit late on Friday.

Other spam monitors

A check against 86 blacklist sites produced 82 responses, all green.