A Mail Client—also known as a Mail User Agent (MUA)—is a dedicated software application installed on a desktop, laptop, or mobile device that allows users to send, receive, organize, and manage email.
Unlike Webmail, which runs inside a web browser and relies on server-side rendering, mail clients run natively on operating systems and connect to mail servers using standard protocols like IMAP, POP3, and SMTP.
Mail clients rely on distinct networking protocols to perform different tasks:
| Protocol | Default Ports (Encrypted) | Direction | Function |
|---|---|---|---|
| IMAP4 | `993` (TLS/SSL) / `143` (STARTTLS) | Server → Client | Synchronizes folders, flags, and emails across multiple devices in real time. |
| POP3 | `995` (TLS/SSL) / `110` (STARTTLS) | Server → Client | Downloads emails to a single device and (optionally) deletes them from the server. |
| SMTP | `465` (Implicit TLS) / `587` (STARTTLS) | Client → Server | Dispatches outbound messages from the client to the submission server. |
| Mail Client | Operating Systems | Key Features | License |
|---|---|---|---|
| Mozilla Thunderbird | Windows, macOS, Linux, Android | Open-source, tabbed interface, extensive add-on ecosystem, native OpenPGP support. | Free / Open Source |
| Microsoft Outlook | Windows, macOS, iOS, Android | Enterprise integration, built-in calendar and task manager, Exchange/OAuth2 support. | Proprietary |
| Apple Mail | macOS, iOS, iPadOS | Deep OS integration, S/MIME support, Privacy Protection, clean user interface. | Proprietary (Free with OS) |
| eM Client | Windows, macOS | Built-in chat, PGP encryption wizard, calendar, and task management. | Freemium |
| K-9 Mail / Thunderbird Mobile | Android | Advanced IMAP push support, lightweight resource footprint, privacy focused. | Free / Open Source |
When configuring a mail client for an account hosted on Telenegar or custom mail servers, adhere to these security standards:
# **Enforce SSL/TLS:** Always configure clients to use encrypted connection ports (`993` for IMAP, `465`/`587` for SMTP). Avoid unencrypted legacy ports (`110`, `143`, `25`). # **Use App Password / OAuth2:** For accounts protected by Multi-Factor Authentication (MFA), use OAuth2 authorization tokens or dedicated application passwords rather than account primary credentials. # **Match Sender Domain (Alignment):** Ensure the outgoing address configured in the client matches your domain's [[email:dns-configuration:spf|SPF]] and [[email:dns-configuration:dkim|DKIM]] identity to prevent messages being flagged as [[email:security:spoofing|Spoofed]] or ending up in [[email:security:spam|Spam]].
If a mail client fails to connect or send mail, test server accessibility using Telenegar Tools: