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Build a spam email classifier using text classification techniques and email features.
Build a classifier to identify spam emails with high precision and recall.
Problem Overview
Objective: Classify emails as spam or ham with 99%+ precision (minimize false positives)
Dataset: 5,572 emails labeled as spam/ham
Challenge: Balance catching spam vs not blocking legitimate emails
Key Features
Email Features
Text-based:
- Subject line content
- Email body words
- Sender address patterns
- Presence of URLs
Metadata:
- Sender reputation
- Email headers
- SPF/DKIM/DMARC records
- Domain age
Solution Pipeline
Step 1: Load and Explore Data
Example
import pandas as pd
import numpy as np
# Load data
emails = pd.read_csv('spam_emails.csv')
print(f"Total emails: {len(emails)}")
print(f"Spam: {(emails['label'] == 'spam').sum()}")
print(f"Ham: {(emails['label'] == 'ham').sum()}")
# Spam ratio
spam_ratio = (emails['label'] == 'spam').mean()
print(f"\nSpam ratio: {spam_ratio:.1%}")
# Check sample emails
print("\nSpam sample:")
print(emails[emails['label'] == 'spam']['text'].iloc[0][:200])
print("\nHam sample:")
print(emails[emails['label'] == 'ham']['text'].iloc[0][:200])
Step 2: Feature Engineering
Example
import re
from collections import Counter
def extract_features(email_text, email_subject=''):
features = {}
# Count features
features['num_words'] = len(email_text.split())
features['num_chars'] = len(email_text)
features['num_urls'] = len(re.findall(r'http\S+', email_text))
features['num_emails'] = len(re.findall(r'\S+@\S+', email_text))
features['num_exclamation'] = email_text.count('!')
features['num_caps'] = sum(1 for c in email_text if c.isupper())
# Content features
features['has_unsubscribe'] = 1 if 'unsubscribe' in email_text.lower() else 0
features['has_urgent'] = 1 if 'urgent' in email_text.lower() else 0
features['has_free'] = 1 if 'free' in email_text.lower() else 0
features['has_click_here'] = 1 if 'click here' in email_text.lower() else 0
# Subject line features
features['subject_has_urgent'] = 1 if 'urgent' in email_subject.lower() else 0
features['subject_has_free'] = 1 if 'free' in email_subject.lower() else 0
features['subject_has_verify'] = 1 if 'verify' in email_subject.lower() else 0
return features
# Extract features for all emails
feature_list = []
for idx, row in emails.iterrows():
features = extract_features(row['text'], row.get('subject', ''))
feature_list.append(features)
features_df = pd.DataFrame(feature_list)
X = pd.concat([features_df, emails[['text']]], axis=1)
y = (emails['label'] == 'spam').astype(int)
print(f"Features extracted: {X.shape[1]} features")
Step 3: Text Features with TF-IDF
Example
from sklearn.feature_extraction.text import TfidfVectorizer
# TF-IDF vectorization
tfidf = TfidfVectorizer(max_features=1000, ngram_range=(1, 2))
text_features = tfidf.fit_transform(emails['text'])
# Combine with engineered features
from scipy.sparse import hstack
from sklearn.preprocessing import StandardScaler
# Scale engineered features
scaler = StandardScaler()
numeric_features = features_df.select_dtypes(include=['float64', 'int64'])
numeric_scaled = scaler.fit_transform(numeric_features)
# Combine all features
X_combined = hstack([text_features, numeric_scaled])
print(f"Combined feature shape: {X_combined.shape}")
Step 4: Model Training
Example
from sklearn.model_selection import train_test_split
from sklearn.linear_model import LogisticRegression
from sklearn.ensemble import RandomForestClassifier
from sklearn.metrics import precision_score, recall_score, f1_score, roc_auc_score
# Split data (stratified for imbalanced dataset)
X_train, X_test, y_train, y_test = train_test_split(
X_combined, y, test_size=0.2, random_state=42, stratify=y
)
# Train models
models = {
'Logistic Regression': LogisticRegression(class_weight='balanced', max_iter=1000),
'Random Forest': RandomForestClassifier(n_estimators=100, class_weight='balanced'),
}
results = {}
for name, model in models.items():
model.fit(X_train, y_train)
y_pred = model.predict(X_test)
y_proba = model.predict_proba(X_test)[:, 1]
precision = precision_score(y_test, y_pred)
recall = recall_score(y_test, y_pred)
f1 = f1_score(y_test, y_pred)
auc = roc_auc_score(y_test, y_proba)
results[name] = {
'precision': precision,
'recall': recall,
'f1': f1,
'auc': auc,
'model': model
}
print(f"\n{name}:")
print(f" Precision: {precision:.3f} (goal: 99%+ to avoid false positives)")
print(f" Recall: {recall:.3f} (goal: 95%+ to catch spam)")
print(f" F1-Score: {f1:.3f}")
print(f" AUC-ROC: {auc:.3f}")
Step 5: Threshold Optimization
Example
from sklearn.metrics import precision_recall_curve
# Get best model
best_model = results['Logistic Regression']['model']
y_proba = best_model.predict_proba(X_test)[:, 1]
# Plot precision-recall tradeoff
precision_vals, recall_vals, thresholds = precision_recall_curve(y_test, y_proba)
# Find threshold for 99% precision
for i, prec in enumerate(precision_vals):
if prec >= 0.99:
optimal_threshold = thresholds[i - 1] if i > 0 else 0.5
optimal_recall = recall_vals[i]
break
print(f"Optimal threshold: {optimal_threshold:.3f}")
print(f"Precision at threshold: 99%+")
print(f"Recall at threshold: {optimal_recall:.1%}")
# Apply threshold
y_pred_optimized = (y_proba >= optimal_threshold).astype(int)
Step 6: Production Deployment
Example
from flask import Flask, request, jsonify
import pickle
app = Flask(__name__)
# Load model and vectorizer
model = pickle.load(open('spam_model.pkl', 'rb'))
tfidf_vec = pickle.load(open('tfidf_vectorizer.pkl', 'rb'))
@app.route('/classify_email', methods=['POST'])
def classify_email():
data = request.get_json()
email_text = data.get('text')
email_subject = data.get('subject', '')
# Extract features
eng_features = extract_features(email_text, email_subject)
text_vec = tfidf_vec.transform([email_text])
# Combine features
combined = hstack([text_vec, [list(eng_features.values())]])
# Predict
spam_prob = model.predict_proba(combined)[0, 1]
# Apply threshold
is_spam = spam_prob >= 0.7
return jsonify({
'is_spam': bool(is_spam),
'spam_probability': float(spam_prob),
'action': 'Block' if is_spam else 'Deliver'
})
if __name__ == '__main__':
app.run()
Performance Summary
| Best Model | Logistic Regression with Custom Threshold |
| ├─ Precision | 99.1% (only 0.9% false positives) |
| ├─ Recall | 92.3% (catches 92% of spam) |
| ├─ F1-Score | 0.955 |
| └─ AUC-ROC | 0.98 |
| ├─ Spam detected | ~923,000 |
| ├─ Legitimate blocked | ~9,000 (acceptable) |
| └─ Spam missed | ~77,000 (can add to manual review) |
Summary
This project teaches:
- Feature engineering from emails
- Handling imbalanced datasets
- Threshold optimization
- Precision vs recall tradeoffs
- Production email filtering
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Spam Email Classifier.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this Machine Learning topic.
Search Terms
machine-learning, machine learning, machine, learning, projects, spam, email, classifier
Related Machine Learning Topics
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