The mail client is where your mail is decrypted, rendered, and read, so its choices matter as much as the server's. A client that loads remote content by default, accepts broken TLS, or stores plaintext carelessly can undo protections elsewhere. This article lists the criteria that matter for a security-focused setup and compares common options against them.
What to look for
- TLS enforcement and certificate checking. The client should verify certificates by default and refuse to connect when verification fails. An "accept any certificate" option should exist only behind a clear warning, if at all.
- Modern authentication. App passwords are fine for ITProMail. Where a provider supports OAuth, it is generally preferable, because it avoids a long-lived password stored in the client.
- Remote content control. Blocking remote images and content by default, with per-message allowance, is one of the most useful privacy settings. See tracking pixels.
- End-to-end encryption support. For PGP, look for built-in OpenPGP support or a well-maintained integration with GnuPG. For S/MIME, look for native certificate handling.
- Contained HTML rendering. HTML mail should render without running scripts, and links should show their real destinations before you click.
- Server-side filtering. Filters that run on the server keep rules in one place and apply them on every device. ITProMail provides Sieve filtering under Account > Filters.
- Local storage and updates. Find out whether messages are cached in plaintext and whether the device uses full-disk encryption. Regular security updates matter more than feature count.
- Auditable code. Open source makes it easier to verify what a client does with your mail. It does not guarantee that the project is well maintained, so check the release history too.
Comparison
The table below describes general tendencies. Defaults and features change between releases, so check the current version before relying on any single cell.
| Client | Remote content | PGP | S/MIME | Platform |
|---|---|---|---|---|
| Thunderbird | Blocked by default, adjustable in privacy settings | Built-in OpenPGP | Supported | Desktop, cross-platform |
| K-9 Mail / Thunderbird for Android | Remote content controls available | Depends on release, check current docs | Limited | Android |
| aerc | Text-first, HTML through a configured filter | Via GnuPG | Via external tools | Terminal, Unix-like |
| mutt / neomutt | Text-first, HTML through a configured filter | Via GnuPG | Via external tools | Terminal, Unix-like |
| Apple Mail | Privacy protection options for remote content | Via third-party plugin | Supported | macOS, iOS |
| Outlook | External images blocked by default | Not native | Supported | Windows, macOS, web |
Desktop, mobile, and terminal
Thunderbird is the most complete desktop option for a security-minded user, with built-in OpenPGP, remote content controls, and solid IMAP support. Apple Mail and Outlook are reasonable choices on their own platforms, but check their PGP story before relying on it. Terminal clients such as aerc and mutt or neomutt suit people who want text-first mail and scriptable workflows. They take more setup, particularly for PGP through GnuPG, but they display less by default.
On Android, K-9 Mail and Thunderbird for Android are the main open-source choices. Check each release's documentation for PGP support, because it has changed over time.
Things that matter more than the client
- Use an app password per device rather than your login password. See app passwords.
- Keep each device encrypted and locked.
- Keep the client updated, including on phones.
- Review which accounts and devices are signed in, and revoke sessions you do not recognise.
Setup guides
For ITProMail-specific configuration, see the guides for Thunderbird, Apple Mail, Android, Outlook, mutt, and aerc. For encryption, see PGP. Start with the criteria above, choose the client that fits how you work, and set it up with an app password and remote content blocked.