Malicious URL detection is a significant area of research in cybersecurity and involves identifying URLs that lead to malicious websites. Machine learning can be a powerful tool in this domain, as it can automatically learn and make predictions or decisions without being specifically programmed for that task.

Here’s an overview of how you might apply machine learning for malicious URL detection:

1. Data Collection: You’ll need a dataset of URLs, categorized as either malicious or benign. This data can be obtained from various sources, including public datasets or security organizations.
2. Feature Extraction: Transforming the raw URLs into a format that can be fed into a machine learning model is essential. You might include features like the URL’s length, the number of subdomains, presence of specific keywords, use of non-standard ports, etc.
3. Data Preprocessing: This might involve cleaning the data, handling missing values, and splitting it into training and testing sets.
4. Model Selection: You can experiment with different machine learning models like Decision Trees, Random Forests, SVMs, or Neural Networks. The selection might depend on the nature of your data and the required performance metrics.
5. Training and Tuning: Train the model on the training data and fine-tune it using techniques like cross-validation to find the optimal hyperparameters.
6. Evaluation: Assess the model’s performance using metrics like accuracy, precision, recall, and F1-score on the validation and test datasets.
7. Deployment: Implement the model into a real-time system to analyze and categorize URLs as they are accessed.
8. Continuous Monitoring: Continuously monitor and update the model as new malicious URLs are discovered and the landscape evolves.

In terms of making sure that related communications (such as email notifications regarding detected malicious URLs) do not go to spam, it’s critical to adhere to best practices for bulk email sending. This includes using verified sender addresses, ensuring that recipients have opted in to receive the emails, including a clear and easy opt-out method, and avoiding content that might trigger spam filters.

Note that designing and implementing a malicious URL detection system using machine learning is a complex task and should be handled by professionals with experience in both machine learning and cybersecurity. If you are planning to work on this, you might consider collaborating with experts in these areas or pursuing formal training and certifications.