Well, they state they don't sell any email addresses[1], and delete any data after a certain amount of days, only using it for averages and anonymous stats. Looking at the other comments here and in the past[2] the site has been very helpful to quite a few people over quite a few years.

I'd also say it's a bit weird to reduce OVH, which is arguably the largest European cloud provider, to just protecting spammers and scammers or being pro-spammer. But that's just my opinion based on my experiences, you may consider it to be different.

The company behind it is called WOOBEO, based in France, as listed in their TOS[3]. You can probably look up more information about them. Or you could contact them and ask them directly even[4].

All in all, if you think you have a good reason not to trust this site, or any site like it, it seems simple enough to just decide to not use it, like with any online service. I suppose this is just like any other risk/reward situation, and the reward seems to outweigh the risk for most people.

[1] https://www.mail-tester.com/faq#privacy [2] https://news.ycombinator.com/item?id=10408169 [3] https://www.mail-tester.com/manager/terms-of-service.html [4] https://www.mail-tester.com/contact