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6123
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1 ---
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2 labels:
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3 - 'Stage-Alpha'
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4 summary: 'Spam filtering'
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5 rockspec:
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6 build:
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7 modules:
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8 mod_anti_spam.rtbl: rtbl.lib.lua
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9 mod_anti_spam.trie: trie.lib.lua
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10 ---
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11
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12 This module aims to provide an all-in-one spam filter for any kind of Prosody
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13 deployment.
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14
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15 ## What is spam?
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16
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17 You're lucky if you have to ask! But it's worth explaining, so we can be clear
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18 about what the module does (and does not).
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19
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20 Similar to every other popular communication network, there are people who try
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21 to exploit XMPP for sending unsolicited messages - usually advertisements
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22 for products and services. These people have gathered large lists of user
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23 addresses, e.g. by searching and "scraping" websites for contact info.
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24
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25 If your address has not been discovered by the spammers, you won't receive any
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26 spam. Prosody does not reveal user addresses (except, obviously, to people who
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27 you communicate with). So to avoid it being picked up by spammers, be careful
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28 about posting it unprotected on websites, etc.
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29
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30 However, if get unlucky and your address is discovered by spammers, you may
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31 receive dozens of spam messages per day. mod_anti_spam is designed to filter
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32 these annoying messages to prevent them from reaching you.
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33
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34 ## How does it work?
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35
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36 mod_anti_spam uses a variety of techniques to identify likely spam. Just as
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37 the behaviour of spammers changes, The exact methods used to detect spam may
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38 evolve over time in future updates.
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39
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40 If the sender is in the recipient's contact list already, no filtering will be
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41 performed.
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42
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43 Otherwise, if the sender is a "stranger" to the recipient, the module will
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44 perform some checks, and decide whether to let the message or contact request
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45 through.
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46
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47 ### Shared block lists
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48
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49 mod_anti_spam can subscribe to Real-Time Block Lists (RTBLs) such as those
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50 published by [xmppbl.org](https://xmppbl.org). This is a highly effective
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51 measure to reduce spam from the network.
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52
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53 To enable this feature, you need to specify one or more compatible spam
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54 services in the config file:
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55
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56 ```lua
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57 anti_spam_services = { "xmppbl.org" }
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58 ```
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59
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60 ### Content filters
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61
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62 mod_anti_spam also supports optionally filtering messages with specific
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63 content or matching certain patterns.
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64
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65 A list of strings to block can be specified in the config file like so:
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66
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67 ```lua
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68 anti_spam_block_strings = {
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69 -- Block messages containing the text "exploit"
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70 "exploit";
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71 }
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72 ```
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73
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74 Alternatively, you can specify a list of [Lua patterns](https://lua.org/manual/5.4/manual.html#6.4.1).
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75 These are similar to regular expressions you may be familiar with from tools
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76 like grep, but differ in a number of ways. Lua patterns are faster, but have
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77 fewer features. The syntax is not fully compatible with other more widely-used
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78 regular expression syntaxes. Read the Lua manual for full details.
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79
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80 ```lua
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81 anti_spam_block_patterns = {
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82 -- Block OTR handshake greetings (modern XMPP clients do not use OTR)
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83 "^%?OTRv2?3?%?";
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84 }
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85 ```
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86
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87 There are no string or pattern filters in the module by default.
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88
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89 ## Handling reports
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90
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91 We recommend setting up Prosody to allow spam reporting, in case any spam
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92 still gets through. Documentation can be found on [xmppbl.org's site](https://xmppbl.org/reports#server-operators).
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93
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94 ## Compatibility
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95
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96 Compatible with Prosody 0.12 and later.
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