This is on Fastmail where I have dozens of email addresses that are context based and then to take it even further I almost always use an on-the-fly alias. I have never received an email to the email address in question which I've had for 10 years except for this one instance immediately after visiting Germany.
I traveled with a Verizon locked iPhone 17 and had Verizon international add-on. My phone has nearly no apps on it with the exception of the iOS Fastmail app and a few small open source non-bloated apps.
I do not believe this is a coincidence. Any thoughts on what took place, how this happened?
Additional thoughts and clarification: 1. I checked the raw message and it was indeed sent to an email address that I've never used in a web form and have never received an inbound email to. 2. The email address in question is very unique and isn't something that could potentially just be guessed by spammers. 3. I haven't received an email to this email in question since. 4. The email address in question I have never used an on-the-fly alias (<alias>@<user>.<domain>.<tld>) 5. I didn't click on the link in the email but it looks to be a transactional email originated with Amazon SES to verify my email address. Subject and body is 100% in German including address information, UID (tax id?) number, etc.
It's not beyond reason to guess that you stumbled into some niche ad targeting group, like "US grape juice drinkers who've visited Germany", and your old email identity was transitively linked somehow. Maybe ten years ago that email was about grape juice?
Also, I don't see the connection to Germany?
Just throwing shit at the wall however, no definitive proof one way or another.