Posteo does not allow the use of custom domains, however users may still make use of subaddressing.
Posteo does not accept Bitcoin or other cryptocurrencies as a form of payment, however they do accept cash-by-mail. They also accept credit/debit cards, bank transfers, and PayPal, and claim that PII (personally identifiable information) that they receive in connection with these payment methods is not linked to your account.
+Posteo does not accept Bitcoin or other cryptocurrencies as a form of payment, however they do accept cash-by-mail. They also accept credit/debit cards, bank transfers, and PayPal, and remove PII (personally identifiable information) that they receive in connection with these payment methods.
Posteo supports two factor authentication for their webmail only. You can use either TOTP a Yubikey with TOTP. Web standards such as U2F and WebAuthn are not yet supported.