Mailbox.org

Mailbox Standard compared to ProtonMail Plus:

• Cheaper (€30/yr vs ~€50/yr; if you don't need custom domains, €1/mo)
• More aliases (25 on mailbox, 50 on own domain. Proton has 10 TOTAL - why custom domain aliases are counted against Proton ones does not make sense to me.)
• Support for any number of custom domains AFAICT (Proton Plus supports only one)
• Trial account is not allowed to send emails, so fewer issues with services blacklisting proton.me and protonmail.com for spam (hasn't happened to me, but I have heard of some cases)
• Can use a regular email client (security tradeoff for E2EE messages - but there already were plenty of discussions on whether E2EE has benefits, especially sending mail to other services)