I just took over some new voluntary responsibility of managing the paperwork for the support association („Förderverein“) of my daughter’s primary school. Trying to get an overview over the current topics, I flipped through the recent documents, when I found a printed e-mail from the school’s director. The most surprising thing about that e-mail was that I had never seen it before, although my name and correct e-mail address was clearly visible in the To: field.

I started to wonder: Had I received the message, archived and forgot about it? Was it blocked by the spam filter? Was there something wrong with my mail client? This is how the search started.

My first stop was my mail client. I put all possible combinations of sender name, subject, date etc. into the search box. There were a few mails from the school, but only older ones. Maybe my mail app had some kind of local caching issue, which prevented it from displaying this particular message? I logged on to my web host’s web mail interface. Not having used it at all in the past, I tried finding my way around, repeated the search exercise, browsed through some folders, sorting them by date – no sign of said message. There were newer mails, but not many.

I remembered having sent a test mail to an address that forwards to my wife and myself a few days back, which we had both received, so nothing could have been wrong with the server configuration. Or could it? I quickly sent another one from a different provider and waited for it to be delivered to my inbox. Just a few seconds later, I heard my mail app’s well-known „ding“ sound. Sure enough, there it was. Or was it? Actually, what I just received was an error message in the sending account’s inbox containing the following message:

Host or domain name not found. Name service error for name=mail.goeb.eu type=A: Host found but no data record of requested type

Name service error? Ah, right, I recently moved the DNS servers for goeb.eu over to Cloudflare. Maybe something went wrong in the process of migrating the settings?

Having watched Troy Hunt’s explanations on httpsiseasy.com some time back, and in light of the deprecation of TLS versions 1.0 and 1.1, I wanted to disable these protocols for blog.goeb.eu, which I found no settings for in wordpress.com’s admin interface. So I decided to put goeb.eu on Cloudflare’s free personal plan, which involves using their name servers for the whole domain.

So I logged on to the Cloudflare control panel and found something interesting: My domain did have an MX record, and it did have an AAAA record for my mail server as well, which pointed to the correct IPv6 address (which is why I did receive some e-mail), but for some reason the A record was gone (which is why I did not receive others)! So, for a short period of time, I accidentally only accepted e-mail for all of goeb.eu only via IPv6 – and therefore excluded all senders that relied on IPv4 being available.

After re-creating the A-record and sending another test mail from the account that produced the error above, I confirmed that I was now able to receive mail over IPv4 again. In summary, I conclude that the journey to IPv6 is still far from being complete – at least in Germany.

Funny coincidence: Telling (a less geeky version of) this story to my wife that same evening revealed that she had been surprised that her recent unsubscribing from various newsletters was such a huge success and that she only received very few mails since. She just was a bit surprised that she did not even get some order confirmations or shipping status mails for stuff she recently bought, but did not bother to ask me about it.