Having the same issue here.
The last GOTD email I received was on March 23rd.
To test if the issue was the fault of my e-mail provider, I subscribed yesterday using a secondary e-mail address of a different provider. I did receive the subscription authorization e-mail and verified as directed. Today, no GOTD email to either address. (and just FYI, they are not going to spam folder and I have been receiving them without issue for years)
I'm stumped!
Attempting my own fix, I just unsubscribed from the daily e-mail using the link in the March 23rd email. I will let your database refresh overnight (assuming that's when it occurs) and then resubscribe tomorrow with the hope that may alleviate the problem and delivery will resume.
Despite this issue, I want to say thanks to the team there at GOTD for all your hard work! I hope we can get this issue cleared up. If you need me to test/verify any fix of the delivery for you, feel free to contact me.