[DOC] User guide

(cherry picked from commit 739751904812b6a9b9f3e690a0fa4290bb11e014)

docs/user-guide/antispam.md

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+# Anti-Spam {#1}
+
+This section will explain about how anti-spam works, and peak about antispam training.
+
+### How Anti-Spam Works:
+
+- Anti-Spam feature in Tmail is designed to classify the messages as spam or not  with an configurable score threshold.
+- Usually a message will only be considered as spam if it matches multiple criteria; matching just a single test will not usually be enough to reach the threshold.
+- Spam is reported on a per user base.
+- When a message is classified as spam, it will automatically moved to user's Spam folder
+
+### Anti-Spam training
+
+1. Marking Emails as Spam:
+
+- You can manually mark emails as spam . This action provides feedback to the anti-spam system, helping it learn from user preferences.
+
+2. Whitelisting:
+
+- Conversely, you can mark legitimate emails as not spam or whitelist specific senders. This feedback helps the system refine its understanding of trusted sources.
+
+3. Custom Filtering Rules:
+
+- Tmail allows users to set up custom filtering rules. For example, you can create rules to automatically move emails containing certain keywords to the spam folder.
+
+By actively participating in anti-spam training as above, you contribute to a more accurate and personalized spam filtering experience.