In theory there are alternatives where you do not need to trust the server. The keyword is proxy re-encryption (e.g. [SELS]).
On the other hand schleuder exists today and can be used by normal people (for example without having a custom private key per list, as you need afaik for [SELS]).
The other often overlooked fact about schleuder is that it's also a re-mailer. You can use it in a one-to-many setting, where the external party does only know the cryptographic key and email address of the list and a group of people can communicate with this person using schleuder as the proxy. This is a great alternative to shared mailboxes and a feature that is probably impossible with proxy encryption.
On the other hand schleuder exists today and can be used by normal people (for example without having a custom private key per list, as you need afaik for [SELS]).
The other often overlooked fact about schleuder is that it's also a re-mailer. You can use it in a one-to-many setting, where the external party does only know the cryptographic key and email address of the list and a group of people can communicate with this person using schleuder as the proxy. This is a great alternative to shared mailboxes and a feature that is probably impossible with proxy encryption.
[SELS] https://slagell.info/Adam_J._Slagell/Past_Projects_files/khu...