Lost my phone, so I registered for an account and added my phone.
Started getting large amounts of random spam right after registration; I get 10-20 per day now from just a couple per week.
I have not registered for any other websites recently.
I am fairly sure they are selling e-mail addresses, and who knows what other information to third parties. And not even reputable third parties, but the worst kinds of spammers.
Do not use a real e-mail address or real information. I wouldn't be surprised if they even sold your IMEI and phone information to marketers.
I am owner of www.imeidetective.com project and I can assure you that we never collected emails for money purpose on any of our projects. We hate spam and we don't want to have bad publicity because of this, but we are trying to help.
We are not detectives, we don't investigate anything. This is only our brand name of this service. IMEIdetective project's goal is to allow people to submit their case when lost their phone or when it got stolen. You need to understand that if somebody find the phone and is looking for owner and can't find any information about owner, there is no chance to get your phone back.
This is why we started this project with user submissions. This project was started almost 10 years ago under different domain, but was moved 2-3 years ago to current domain as new brand with multiple languages added to be a global project. We believe that such global project to inform people before buying second hand mobile device or to help find owner is great. I am sorry that you had bad experience with spam, but it seems that somehow people get also new email accounts who used free email service at least once for anything even if this is not publicly accessible. I also receive spam on my email accounts even if I never used it and never published it anywhere.
I wish you all the best!