Fastmail’s 2025 explainer says TLS protects messages in transit, while storage encryption with provider-held keys protects against disk exposure, not a fully compromised server or valid demands for decrypted data. Password-based zero-access encryption limits access to stored mail but does not necessarily protect ordinary external messages when they arrive or copies held by correspondents. Proton’s documentation likewise distinguishes TLS and storage protection for external mail from end-to-end encryption within its service. Choosing an approach requires weighing the relevant threats against search, recovery, and remaining metadata exposure.