====== Desktop & Mobile Mail Clients ======

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 [[email:clients:webmail|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**.

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===== Protocol Architecture =====

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. |

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===== Popular Desktop & Mobile Mail Clients =====

^ 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 |

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===== Key Advantages of Dedicated Mail Clients =====

  * **Offline Access:** Email bodies, attachments, and folder structures are cached locally, allowing reading and drafting emails without an internet connection.
  * **Unified Inbox:** Manage multiple email accounts across different domains and providers within a single unified workspace.
  * **End-to-End Encryption (E2EE):** Native support for [[email:security:email-encryption|S/MIME and OpenPGP]], permitting client-side message signing and payload encryption.
  * **System Notifications & Rules:** Native OS notification integration, local filtering rules, and automated sorting scripts.

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===== Configuration Best Practices =====

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]].

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===== Diagnostics & Connectivity Tools =====

If a mail client fails to connect or send mail, test server accessibility using **Telenegar Tools**:

==== Using Telenegar Tools ====
  * **Port & TLS Check:** Verify that IMAP and SMTP ports are open and responding properly using the [[tools:mailcheck|Telenegar Mail Check Tool]].
  * **DNS Lookup:** Validate MX and mail server hostname resolution using the [[tools:dnscheck|Telenegar DNS Check Tool]].

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===== Related Documentation =====

  * [[tools:mailcheck|Telenegar Mail Check Tool]] — Test client connectivity, port availability, and SMTP response codes.
  * [[tools:dnscheck|Telenegar DNS Check Tool]] — Validate hostname resolution for mail servers.
  * [[email:clients:webmail|Webmail]] — Web-based alternative to dedicated mail applications.
  * [[email:security:email-encryption|Email Encryption]] — S/MIME and PGP configuration in mail clients.
  * [[email:troubleshooting:bounces|SMTP Status Codes & Email Bounces]] — Diagnose connection and sending errors returned to mail clients.
  * [[email:troubleshooting:reverse-dns|Reverse DNS (PTR)]] — Ensure client outbound connections pass server security checks.