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Proton
Empowering you to choose a better internet where privacy is the default. Protect yourself online with Proton Mail, Proton VPN, Proton Calendar, Proton Drive. Proton Pass and SimpleLogin.
Proton Mail is the world's largest secure email provider. Swiss, end-to-end encrypted, private, and free.
Proton VPN is the world’s only open-source, publicly audited, unlimited and free VPN. Swiss-based, no-ads, and no-logs.
Proton Calendar is the world's first end-to-end encrypted calendar that allows you to keep your life private.
Proton Drive is a free end-to-end encrypted cloud storage that allows you to securely backup and share your files. It's open source, publicly audited, and Swiss-based.
Proton Pass Proton Pass is a free and open-source password manager which brings a higher level of security with rigorous end-to-end encryption of all data (including usernames, URLs, notes, and more) and email alias support.
SimpleLogin lets you send and receive emails anonymously via easily-generated unique email aliases.
I have somewhere on the order of 80 accounts on as many websites registered to Protonmail accounts, and I've never once had a website turn me away for the @protonmail.com domain. I exclusively use that domain. I can only remember one specific instance where they had downtime, too - overall they've been very reliable.
I did once have some of my protonmail accounts closed for suspicious activity, multiple years ago - but in their defense I was being pretty suspicious. I emailed support from my main account, explained the situation, and they unlocked the accounts for me - never had an issue since.
There definitely are sites that block or restrict accounts using ProtonMail addresses. Obviously social media sites will be more likely to force an account to provide a phone number if one is using a proton mail address compared to for instance, a GMail address. There has been one site I have seen block/restrict ProtonMail outright, and that is Lenovo. It is not possible to actually make purchases from Lenovo directly if the account's email is a ProtonMail address. Too be fair though, that is the only site I have seen any explicit account blocks/restrictions.
They block both @protonmail.com and @pm.me aliasesl?
It seems I did not try making a Lenovo account with the pm.me alias address. I did use a protonmail.com address when tried before swapping to making an account using a Tutanota address and attempting to replay the purchase sequence. I don't remember the conversation I had with support when they deduced the error to protonmail addresses not being eligible for purchases for not "being verifiable" despite the fact that payment and billing information is also provided in a purchase. I don't remember if the support technician claimed that the pm.me alias would also be blocked, but for some reason I never tried it.