Summary
Native cross platform apps available. Paid plans enable custom domains. No third-party email clients are supported, users need to use the wide range of native apps. Based in Germany, founded in 2011.
I started my Tutanota journey 2 years back. Although it has a very simple UI but the strong security it offers means it provides strong competition to ProtonMail (a Switzerland based popular private & secured email provider). Despite the lack of features, I find it fulfill my basic needs for email and generally I do not face any huge issues using it.
Their native apps work as good as their webmail and offers everything you need in an email, such as creating filters, aliases and you can even configure your custom domain -- provided you pay for a plan. They also offers catch-all for all your custom domains that translate to unlimited aliases (however you're limit only to 5 aliases, depending on the plan you subscribed, for sending emails).
Pricing has to be their most attractive selling point. Anyone can pay for just $12/year for a premium account which comes with 1Gb storage, 5 aliases and a custom domain. Compared to other competitors which starts off their plan for at least $3/month, this is quite a steal! However there's an interesting twist to this, starting this month (June 2023) the price plan has been revised and they no longer offer the basic plan of $12/year, now it starts off with $3/month (if you pay annually) for a bigger storage and more aliases, along with other features such as unlimited calendars which I do not use much.
In a nutshell, Tutanota still is a very good email provider if you value privacy and security, and you can even signup for a free plan which cost you nothing! The only caveat is that there's a 6 months inactivity period which means your account might be marked inactive and the only way to get in, is by paying for a premium if that's the case.