How can you identify the source of unsolicited emails and prevent data leaks?
Matthew Whittaker
Co-founder & CTO, Suped
Published 17 Jun 2025
Updated 16 Aug 2025
6 min read
Unsolicited emails, often referred to as spam or junk mail, are not just annoying, they pose significant security risks. They can be gateways for phishing attacks, malware distribution, and broader data breaches. Understanding how these emails find their way to your inbox is the first step in protecting your digital presence and preventing sensitive information from being exposed.
The increase in unsolicited communications highlights a growing threat to both individuals and organizations. It's crucial to adopt a proactive stance, combining technical solutions with user awareness. My goal is to outline practical steps you can take to identify the origins of these unwanted messages and fortify your defenses against potential data leaks.
Dealing with unsolicited emails goes beyond simply deleting them. It involves understanding the methods spammers and malicious actors use, from sophisticated phishing campaigns to exploiting data breaches. By learning to identify these threats, you can significantly reduce your exposure and safeguard your data.
Identifying the source of unsolicited emails
Identifying the source of unsolicited emails often starts with a close examination of the email itself. Spammers and phishers frequently employ various tactics to bypass filters and trick recipients. Always be suspicious of emails from unknown senders, especially if they contain generic greetings, urgent requests, or unusual attachments.
Look closely at the sender's email address. Often, these addresses will have slight misspellings of legitimate domain names or come from entirely unrelated domains. Hovering over links without clicking them can reveal the true destination URL, which might differ from the text displayed. These subtle cues are often the first giveaways.
For more advanced identification, you can analyze email headers. These headers contain a wealth of information, including the sending IP address and mail servers that handled the message. While technical, this data can help trace the email's path and sometimes even pinpoint its origin. Organizations can use email security protocols like DMARC to help detect forged sender addresses.
Red flags for unsolicited emails
Generic greetings: If an email addresses you as "Dear customer" or a similar non-personal salutation, it's a common sign of a bulk, unsolicited message or even a phishing attempt.
Suspicious sender address: Check the full email address, not just the display name. Look for misspellings, strange domains, or long, random character strings.
Unexpected attachments or links: Do not open attachments or click links from unknown or suspicious emails. Always hover over links to preview the URL before clicking.
Urgent or threatening language: Scammers often try to create a sense of urgency or fear to pressure you into immediate action, such as claiming an account will be closed or there is a security breach.
Poor grammar and spelling: Professional organizations rarely send emails riddled with grammatical errors or typos. This is a tell-tale sign of a scam or low-quality spam.
Common ways email addresses are leaked
One of the most common reasons you receive unsolicited emails is that your email address has been exposed in a data breach. Companies and services you use might experience security incidents, leading to their customer databases, including email addresses, falling into the wrong hands. Once breached, these addresses are often compiled into lists and sold on the dark web or to other spammers.
Another prevalent method is email address harvesting. Spammers use automated bots to scrape email addresses from publicly accessible websites, forums, social media profiles, and even embedded email addresses in web pages. This includes addresses that are visibly listed or part of online directories.
Some organizations also share or sell customer data to third-party marketing companies, often buried in their privacy policies or terms of service that many users don't read thoroughly. While this may not be a "leak" in the malicious sense, it still results in unsolicited emails. Additionally, signing up for newsletters or services without proper double opt-in processes can lead to your address being added to various mailing lists, sometimes without your full consent.
I often suggest using unique, tagged email addresses for different online registrations. For example, if your email is you@example.com, you can sign up for a service as you+service@example.com. If you then receive an unsolicited email to you+service@example.com, you immediately know which service was the source of the leak or data sharing. Many email providers, including Gmail and Outlook, support this plus-addressing feature.
How email addresses are leaked
Data breaches: Compromised databases from legitimate services you've signed up for. Cyberattacks often lead to this.
Public harvesting: Automated bots (spambots) collecting addresses from websites, forums, or social media.
Third-party sharing: Companies sharing or selling your email information to other entities, often permitted by their privacy policies. Services exist to help remove your email from data brokers.
Malware/viruses: Infected computers can expose contact lists or other personal data to attackers, leading to unsolicited emails from your compromised contacts.
Initial detection methods
Email plus addressing: Using unique email aliases (e.g., you+service@domain.com) for different sign-ups helps pinpoint the leak source.
Monitor public exposure: Regularly check if your email address appears on public websites or forums where it shouldn't.
Breach notification services: Sign up for services that alert you if your email address is found in known data breaches.
Review privacy policies: Be mindful of what information you share and how it might be used by companies, opting out of data sharing where possible.
Preventing unsolicited emails and data leaks
Preventing unsolicited emails and data leaks requires a multi-layered approach, combining user vigilance with robust technical safeguards. One of the most effective strategies is to bolster your email authentication. Protocols such as DMARC, SPF, and DKIM work together to verify that incoming emails are legitimate and prevent spoofing or impersonation of your domain.
Implementing a DMARC policy, even with a basic p=none setting, allows you to receive reports on email authentication failures. These reports provide insights into who might be attempting to send emails using your domain, helping you identify potential abuse or misconfigurations. Over time, you can strengthen your policy to p=quarantine or p=reject to instruct recipient servers on how to handle unauthenticated mail. For more information, you can read the FTC's guide on avoiding phishing scams.
Beyond authentication, actively monitoring email blocklists (or blacklists) and your domain's reputation is vital. If your domain or IP address ends up on a blocklist due to suspicious activity, it will severely impact your legitimate email deliverability. Regular checks and quick action to address any listings are crucial.
Finally, user education remains a cornerstone of prevention. Train yourself and your employees to recognize phishing attempts, identify suspicious email domains (or spamtrap networks), and understand the risks associated with clicking unknown links or opening attachments. A strong human firewall complements all technical measures.
Proactive defense against unsolicited emails
To effectively combat unsolicited emails and prevent data leaks, it's essential to combine vigilance with technological solutions. Regularly auditing your email security settings, maintaining updated software, and being critical of unexpected communications are ongoing responsibilities.
Implementing strong email authentication, such as DMARC monitoring, not only protects your domain from being used for malicious purposes but also helps you gain visibility into potential threats targeting your recipients. Consistent monitoring of your email deliverability and sender reputation allows you to address issues before they escalate.
By understanding the sources of unsolicited emails and proactively implementing preventative measures, you can significantly reduce your risk of falling victim to phishing scams, malware, and data exposure. Protecting your inbox is a continuous effort that yields substantial benefits for your overall digital security.
Views from the trenches
Best practices
Actively use unique, tagged email addresses (e.g., yourname+company@domain.com) when signing up for services to easily identify the source of any unwanted email.
Regularly check breach notification services to see if your email address has appeared in a known data breach, and change passwords immediately.
Implement strong email authentication protocols like DMARC, SPF, and DKIM to prevent unauthorized use of your domain and identify spoofing attempts.
Educate yourself and your team on how to spot phishing emails by verifying sender details, scrutinizing links, and recognizing suspicious content.
Utilize robust spam filters provided by your email service or third-party solutions to automatically filter out unsolicited messages.
Common pitfalls
Clicking unsubscribe links in suspicious emails can confirm your address is active, leading to more spam instead of less. Always mark them as spam instead.
Publicly posting your primary email address on websites or social media, making it easy for spambots to harvest.
Not regularly reviewing the privacy policies of services you use, inadvertently consenting to data sharing with third parties.
Assuming your email provider's default spam filters are sufficient; they can miss sophisticated phishing or spam campaigns.
Neglecting to monitor your domain's reputation or check for blocklist listings, which can impact your legitimate email deliverability.
Expert tips
Consider setting up a dedicated 'sacrificial' email address for online registrations that you expect to generate a lot of marketing emails or potential spam.
For organizations, conduct regular phishing simulation exercises to train employees on identifying and reporting suspicious emails effectively.
Leverage DMARC aggregate reports to gain detailed insights into email authentication failures and potential abuse of your domain, allowing for proactive remediation.
Implement a 'zero trust' approach to email: assume every email is potentially malicious until verified, especially if it demands immediate action or sensitive information.
If using Gmail, remember that dots in your email address (e.g., john.doe@gmail.com vs. johndoe@gmail.com) are ignored, but some spammers might not normalize them, which can also help track leaks.
Marketer view
Marketer from Email Geeks says practices like sending unsolicited emails without proper acquisition methods really give marketing a bad name, and these messages should be mass reported.
December 1, 2021 - Email Geeks
Expert view
Expert from Email Geeks says you should try your local Data Protection Agency if you have no one else, as they will investigate such practices and can result in legal actions.
Gmail and 
Outlook, support this plus-addressing feature.
