Member Avatar for killer88

Can i develop spam filter in C# ? if is it so , where do i start ?

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For : Yes - you can build a spam filter in C#. Break the work into stages: ingest and parse messages (headers + body), normalize and clean text (strip HTML, decode encodings), extract signals (tokens, n-grams, URL counts, header anomalies, attachment flags, sender reputation), then apply a fast rule-based scorer for quick wins and a statistical classifier once you have labeled data. Start with simple rules as suggested, supplement them with external reputation/blacklist checks like mentioned, and use .NET string/regex APIs as pointed out.

A minimal C# example to show tokenization + a rule scorer:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

int ScoreText(string text, IDictionary<string,int> rulePoints)
{
    if (string.IsNullOrWhiteSpace(text)) return 0;
    var cleaned = Regex.Replace(text, "<.*?>", " ").ToLowerInvariant(); // crude HTML strip
    var tokens = Regex.Split(cleaned, @"\W+").Where(t => t.Length > 2);
    int score = 0;
    foreach (var t in tokens)
    {
        if (rulePoints.TryGetValue(t, out var pts))
            score += pts;
    }
    return score;
}

// sample rules and usage
var rules = new Dictionary<string,int> { { "free", 5 }, { "lottery", 10 }, { "unsubscribe", -1 } };
int s = ScoreText(emailBody, rules);

Next steps and practical notes: convert tokens into numeric features (TF, TF-IDF, n-grams, header flags) and try simple classifiers (Naive Bayes or logistic regression); in .NET you can integrate ML tooling when you’re ready. Use a realistic labeled dataset for training and evaluate with precision and recall (not just overall accuracy) so you control false positives. Add logging, a whitelist and a user-complaint feedback loop so misclassifications get corrected and models retrained. Layer defenses: reputation checks, SPF/DKIM/DMARC verification, rate limits and CAPTCHAs on forms. Be cautious about privacy and legal rules before sending message content to third-party services, and plan for periodic retraining because spam tactics change.

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Member Avatar for Ancient Dragon

I can't tell you how to check for spam in email, but StopForumSpam has an API that lets you can search by ip address, email address or username. This has stopped probably 99% of the spam I got before I started checking on that site. I see no reason why it won't work for emails as well as web sites.

Edited by Ancient Dragon
Member Avatar for Ketsuekiame

A spam filter, at its basic level, is simply a set of rules applied to your data and it scores points based on those rules.

For example;
1. Does this address exist in the CBL = 1000 points
2. Does the subject contain "$1,000,000" = 20 points
3. Does the body contain "You have won the lottery!" = 50 points
4. Do I know this email address personally? = -20 points

Then you total up the scores and see if it is above your threshold.

To do this in C# would be pretty straightforward, string search and the like. The actual application integration might actually be more difficult.

Member Avatar for killer88

could anyone please send some reference links for string manipulations ? like the whole body of text can be divided into tokens. sort of something.

Member Avatar for ddanbe

We aim to please. MSDN should be your friend. Here is The String class, all the string manipulation you want! Happy programming.

Edited by ddanbe because: typo
Member Avatar for killer88

thanks man :)

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