Which secure email client offers the best mobile experience and cross-device syncing?

1. Canary: the polished mobile champion that also sells the sync story

Canary is presented across vendor materials and third‑party roundups as an app built for mobile workflows with “copilot” AI, unified inbox, and explicit cross‑platform syncing that pushes preferences, signatures and encrypted mail across devices, and the product site and affiliated guides repeatedly claim PGP, biometric locks and secure cloud sync as core features ^{[1] [2] [3]}. TechRadar and privacy guides that surface Canary likewise note its fast IMAP performance and usability on both mobile and desktop, which is why Canary is frequently recommended when the goal is a secure client that “just works” on phones and laptops ^{[9] [3]}. Those endorsements come with an implicit agenda: many of the sources praising Canary are either the vendor’s own blog or marketing‑adjacent guides, so the strong sync narrative should be accepted but cross‑checked in independent tests before committing critical workflows ^{[1] [2]}.

2. Proton Mail: the security-first mobile vault with different syncing priorities

Proton Mail repeatedly appears in reporting as the go‑to if “security above all” is the criterion—its mobile apps implement end‑to‑end and zero‑access encryption so content cannot be read by the provider, and features such as tracker blocking and password‑protected messages are highlighted in multiple reviews ^{[4] [5]}. That model gives ProtonMail a clear advantage when confidential correspondence is non‑negotiable, but it also means sync behaves differently: zero‑access E2E setups and key management can complicate seamless state syncing across many devices compared with cloud‑backed clients (reporting notes Proton’s strong encryption but does not offer head‑to‑head latency or UX metrics) ^{[4] [5]}. For users who demand both strong encryption and instant desktop–mobile parity, Proton’s model may require tradeoffs or extra setup.

3. Thunderbird and local‑first clients: control and offline fidelity at the expense of mobile polish

Open‑source Thunderbird and similar desktop‑centric clients score high for local storage, configurability and security hygiene, which makes them ideal for users who want tighter control over message storage and fewer cloud dependencies ^{[6] [7]}. Reporting suggests Thunderbird has mobile iterations and remains a stalwart for people who value local archives, but community sources and roundups warn that truly frictionless cross‑device syncing—especially for mobile push and unified cloud preferences—remains a weaker area compared with cloud‑centric mobile apps ^{[6] [7] [8]}. For teams and heavy mobile users, that can translate into more manual setup or reliance on third‑party sync bridges.

4. The practical verdict: pick by priority, not by hype

If the top priorities are mobile polish, unified inbox, and effortless cross‑device parity, the evidence points to Canary as the best fit in current reporting—subject to the usual caveat that much of the positive material originates with the vendor or allied reviews and should be validated in independent testing ^{[1] [2] [9]}. If end‑to‑end confidentiality is the absolute requirement, Proton Mail’s mobile apps provide the most robust encryption posture even if that model complicates seamless cloud‑style syncing ^{[4] [5]}. For users who want absolute local control or who run large, offline archives, Thunderbird and local clients remain the sensible choice, but expect more manual work to achieve the same mobile convenience ^{[6] [7] [8]}. The reporting does not supply a single, vendor‑neutral head‑to‑head usability benchmark of mobile sync latency or failure rates, so final selection should be informed by personal testing against these tradeoffs ^{[7] [10]}.