Maybe mail attachements could be stored encrypted by protonmail on a users cloud storage space to conserve protonmail serverstorage, costs and possibly increase reliability for the storage of the text in the message.
The chosen cloud storage could be the users own server like a Synology workstation cloud or some other cloud storage service (dropbox, google or whatever) set with appropriate access parameters to the encrypted data in some way in your Protonmail account.
Obviously data loss of attachments could happen if this is allowed so user should be warned.
Time limitation for mail access should work. Protonmail should try to delete stored attachment mail info if set expiration date is due.
If cloud is not reachable any more (due to for instance disconnection) all protonmail "keys" to be able to decrypt this information (after set expiration date) should at least be deleted.
Anonymous
Maybe mail attachements could be stored encrypted by protonmail on a users cloud storage space to conserve protonmail serverstorage, costs and possibly increase reliability for the storage of the text in the message.
The chosen cloud storage could be the users own server like a Synology workstation cloud or some other cloud storage service (dropbox, google or whatever) set with appropriate access parameters to the encrypted data in some way in your Protonmail account.
Obviously data loss of attachments could happen if this is allowed so user should be warned.
Time limitation for mail access should work. Protonmail should try to delete stored attachment mail info if set expiration date is due.
If cloud is not reachable any more (due to for instance disconnection) all protonmail "keys" to be able to decrypt this information (after set expiration date) should at least be deleted.