What is spam email?

Spam email (or just “spam”) is unsolicited messages sent out in bulk by email, usually for commercial purposes. 

The term spam originated from a Monty Python sketch about the canned pork product, Spam.

Is spam dangerous?

Spam emails are usually a nuisance rather than dangerous, although they can potentially include links to malware or phishing websites.

It’s also worth noting that spam creates a devastating carbon footprint. A 2008 study by Mcafee Virus found that the 62 trillion spam messages sent every year (a staggering 78% of all emails sent) used 33bn kilowatt-hours (KWh) of electricity and caused around 20 million tonnes of CO2e per year. 

Interestingly, around 80% of the electricity consumed was used reading and deleting spam and searching through spam folders to find emails sent there by accident, while 16% was used by spam filters. Just 4% of spam’s emissions were linked to the creation and sending of spam emails.

How do spammers get your email address?

Spammers can obtain your email address from a variety of sources, but the most common ones are:

Data breaches

Databases containing email addresses are leaked or stolen with alarming regularity and are often sold to spammers or simply published on the internet.

Many of these also contain details such as passwords, so it’s always worth checking on websites such as haveibeenpwned.com to ensure your email address has not been included in such a data breach.

Learn what to do if you are the victim of a data breach

Purchased lists

Unscrupulous websites and internet businesses sometimes sell lists of their users or customers’ email addresses to spammers, who then sell these lists on or swap them with other spammers.

Web scraping

Much like Google does, scammers often simply scrape the web for anything that looks like an email address (such as a text string with an @ symbol in it) and add it to a database.


Sending emails is basically free, so scammers sometimes just send out thousands upon thousands of emails to semi-randomly generated email addresses (randotextstring@ gmail.com or hotmail.com). 

It’s also quite easy to guess email addresses based on common names (such as john.smith123@yahoo.com). 

How do email spam filters work?

All commercial email services, including Proton Mail, use automatic spam filters to shield their users from the torrent of junk emails that would otherwise arrive in their inboxes. Our smart spam filters use a number of techniques to detect spam and will learn from emails you Move to spam or mark as not spam (Move to inbox from the Spam folder). 

Blacklist filters

Proton Mail maintains a block list of IP addresses and email addresses known to belong to spammers. 

Subject-line filters

Unlike most email services, Proton Mail cannot read the contents of emails to detect spam. But we can examine subject lines for trigger words or phrases, such as “discount,” “limited time”, or “offer”. 

Subject lines in a language different from the one you have selected in settings may also be regarded as suspicious (so it’s a good idea to check your spam folder if you are expecting to receive this kind of mail).

Header filters

Email headers can contain valuable clues that can be used to detect spam emails, such as whether the email is a copy of a group of emails sent at the same time to a particular group of recipients. 

Learn more about how our encrypted email works

Bayesian Filter

A Bayesian filter is a smart filter that learns from the emails you send to spam or mark as not spam, automatically creating custom spam rules for your inbox. For example, if you mark a message from a certain sender as spam, a new rule-based filter is created for your account, and all future messages from that sender will be sent to your spam folder. 

Content filters (not used by Proton Mail)

Other email services commonly use content filters, but not Proton Mail. This is because they rely on reading the content of your emails, which Proton Mail does not have access to.

These filters scan the content of emails for trigger words. With more text to scan than just the subject line, these typically look for multiple uses of the trigger word. They may also look for emails that contain language of an inappropriate or sexual nature.

How to ensure emails don’t end up in spam

It is inevitable that an automated filter system will make mistakes and send legitimate emails to your spam folder (or miss spam in your inbox). You can help ensure this doesn’t happen in two ways.

Use smart filters

Proton Mail uses a smart (Bayesian) filter to intelligently create rules for your account. If you find an email in your spam folder that shouldn’t be there, simply select it and click the Move to inbox button to move the email back into your inbox and mark it as not spam. 

Move to inbox

Similarly, you can mark emails in your inbox as spam using the Move to spam button. This will send it straight to your spam folder and add the address to your Block List.

Move to spam

Our smart filters will learn from these actions and create new filter rules based on them. To view or modify these rules, sign in to your account and go to SettingsGo to settings → Proton Mail → Filters → Spam filters.

Here, you can also manually add or remove email addresses from your Allow List or Block List.

Spam filters

Learn more about spam filtering, Allow Lists, and Block Lists

Using custom filters

For even greater control over your emails, you can create both simple custom filters and more advanced sieve filters.

Custom filters

These custom filters allow you to filter emails using a wide range of criteria and specify what will happen to them, such as moving filtered emails to your spam folder or ensuring they always arrive in your inbox.

Learn more about how to use filters

Learn how to create an advanced sieve filter 

How to beat spam with a disposable email address

You can reduce the amount of spam that arrives in your inbox using disposable email addresses. 


All Proton Mail users (including users with free accounts) can create an unlimited number of +aliases using the “+” symbol after the username in your email address. 

There are two ways you can use this to defeat spam:

1. Use a +alias whenever a suspicious website (or just one you have no wish to hear from again) asks for your email address. For example, alice.user+spam@proton.me. You can then create a custom filter to automatically send all emails sent to that address to your Spam folder.

2. Use custom +aliases for each website you give your email addresses to. For example, you could use something like alice.user+washingtonpost@proton.me for your Washington post subscription. If you receive an email to this address from anyone other than the Washington Post, you will know they either sold your data or experienced a data breach.

Additional addresses and custom addresses

Users with a paid plan can have up to five additional addresses with any Proton Mail domain (@protonmail.com, @pm.me, @protonmail.ch, or @proton.me). If you subscribe to a paid plan and have your own domain name, you can also create additional addresses using your domain (for example, spam@yourdomain.com)

As with +aliases, you can use one of these addresses for websites you don’t want to hear from again, and filter anything sent to that address into your spam folder. 

Learn more about types of email addresses and aliases

Never answer spam email

It may be tempting to reply to spam emails with a torrent of abuse, but all that is likely to achieve is alerting the spammer that your email address is legitimate, active, and can be targeted with yet more spam!

Do not attempt to unsubscribe from spam email

Most marketing emails and newsletters include an unsubscribe link that you can use to opt out of receiving communications from that sender. If you have trouble finding such a link, Proton Mail offers our own built-in unsubscribe feature, which automatically initiates the unsubscribe routine for that mailing list.

Legitimate companies will respect your preferences, so this can be very useful for unsubscribing from legitimate but unwanted emails.

Learn more about how to unsubscribe from newsletters

However, for emails that do not come from a legitimate source, asking to unsubscribe will not only be ineffective, but, as with answering spam emails, it will confirm that your email address is valid and active. This will likely result in you receiving even more spam.

Final thoughts

Spam email is annoying but rarely more than that. Proton Mail’s filters will shield you from most spam, and with custom filters, disposable email addresses, and a little common sense, you have the tools needed to defeat spam and take control of your inbox.

Frequently asked questions

Can I get a virus from spam?

Most spam is harmless, but some spam emails do contain links that will download malware onto your system or send to a phishing website. 

How do I block an email address?

When you mark an email as spam, it is automatically added to your spam filters Block List. To manage your spam filters in Proton Mail, sign in to your account and go to SettingsGo to settings → Proton Mail → Filters → Spam filters.

What is phishing?

Phishing is a technique used by criminals to obtain victims’ usernames, passwords, and financial details. Much like regular spam, it usually involves sending out unsolicited emails, but these are forged to appear as if they come from a legitimate website (such as a bank). 

If you click on the link provided, you will be taken to a forged website and invited to enter your login credentials, bank details, and the like. 

Learn more about how to prevent phishing attacks

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