We've just been alerted to the fact that 3 email providers (hotmail.com, msn.com, and comcast.com) have started using using a blacklist system that is blocking all emails that originate from the company where our servers are hosted (Linode.com).
This means that if you send to anyone that has one of those companies providing them email your email will bounce back as undeliverable.
The problem is due to the fact that that these companies are using a blacklist that has, at best, questionable tackticks (they will allow you to pay a 'bounty' to get off their blacklist - which is not a reputable way to run a blacklist).
None of our servers have ever individually been flagged as being a source of spam or flagged on an email blacklist, so the issue is outside our immediate control.
We are working with our server host Linode to find a way to resolve this (without paying blackmail bounties). Usually Linode technitians are able to quickly identify a solution to this issue; however, due to the almost global nature of this blacklist, it may take a day or two to resolve.
What you need to do
If you have anyone that you need to communicate with who has an email with hotmail, msn.com, or comcast, you will be unable to send them an email until this issue is resolved. There is nothing that they can do (other than complain to their email providers - or find a new, more reputable email provider).
My suggestion is that you contact these people via other means (phone, text, etc.) until we have this issue resolved.
You will get an email as soon as it is resolved.
We will also post updates on here as well.
This is effecting all of our clients, our own emails and, technically, all emails originating from Linode servers worldwide, so we expect that we should have a resolution to this issue rather quickly; however, due to the fact it involves 2 other parties (email host and the blacklist company), and nobody is likely going to pay the 'bounty', there is a chance it may take a few days to resolve.
If you have any questions about this please feel free to reply and I'll provide whatever answers that I have.