Februar 1st 2019 is “DNS-Flag-Day”.

The Domain Name System DNS is the contact app of the Internet. It allows you to view this website by entering the name “www.cleanmail.ch” into the address bar of your browser, and ensures that emails with @cleanmail.ch are delivered to the right mail server(s).

In the last decades, the DNS protocol has been in constant evolution. Unfortunately there are still quite a lot DNS servers which are still on pre-1999 levels on how they understand the DNS protocol. Current DNS server software uses a series of workarounds to ensure that such aged software still works.

On February 1st 2019 many large providers will turn off these workarounds. Even though 20 years of lead time should be sufficient, and even though there are publicly available tools to check the status of one’s own DNS server, some services and service providers will be surprised on this day.

If you encounter unexpected outages on or after February 1st 2019, there is a certain probability that this is due to the “DNS-Flag-Day”. The infrastructure of Cleanmail is on current levels and thus not affected by this change. However, it could well be that other organisations are affected with the result that they can not send emails to us, or that they can not receive emails sent through us. Please note that this behaviour is outside of the control of Cleanmail and can thus not be whitelisted.

Additional information on the DNS-Flag-Day can be found at https://dnsflagday.net/.