Looks like I coincidentally discovered a serious malfunction in Kraken's main email infrastructure. I tried to withdraw some amount to a newly created bitcoin address. In this case I usually receive an email message containing a confirmation link with a 1 hour's expiration time. Unexpectedly, this email message never arrived. So I checked all my email account settings, deactivated the SPAM detection and any other mail filters. I sent me a dozen differently crafted email messages to myself, i.e. to an email address exclusively created for all my communication with Kraken. They all arrived in perfect condition. Then tried withdrawing to that new bitcoin address again: silence. Tried again: silence. Withdrawing to an old existing bitcoin address works perfectly as this does not require email traffic. They even paid a pretty generous fee of 250+ satoshis/byte for my test transaction. It got included in the very next block.

There is another proof that it's not my email provider that is to blame: I opened a ticket using Kraken's Zendesk frontend, and lo and behold: the ticket receipt arrived at my email inbasket at an instant. This means that the Kraken Support email server works flawlessly while the trading environment's email server is broken.

Don't bother. Email messages from/to Kraken are vanishing into the void at the moment. The only way of communicating with Kraken ist using support.kraken.com. I hope their Zendesk-internal communication is completely independent of the trading platform's email system.