What spam is and 4 rules to keep emails out of spam

Spam is an unsolicited bulk message that the recipient did not want and did not ask for. To keep your emails out of the spam folder, four rules must hold: you send only to people who want your emails, your sending domain has verified SPF, DKIM and DMARC, every email clearly shows it is a commercial communication from a named sender with easy unsubscribe, and people open your content rather than marking it as spam. The rules come from EU law and from the requirements of Gmail, Outlook and other mailbox providers.

In a nutshell

1. Since November 2025 Gmail rejects bulk emails that do not meet its domain authentication requirements.
2. In the EU you may send marketing emails only with prior consent. The exception is existing customers and offers of similar products.
3. Without a verified domain with SPF, DKIM and DMARC records, emails to Gmail and Outlook often do not arrive at all.
4. Every email must be identifiable as a commercial communication, must not conceal the sender and must have a working unsubscribe.
5. In the end, recipients decide whether you reach the inbox: the spam complaint rate must stay below 0.3 %.
6. Remove inactive and invalid addresses regularly, they damage your sender reputation with all other recipients too.

In short: what spam is, who it applies to, what the filter watches and what is at stake

• What spam is: an unsolicited bulk message judged both by the law (consent, label, unsubscribe) and by mailbox providers (recipient behaviour).
• Who it applies to: anyone who sends offers, newsletters or invitations by email, regardless of the number of contacts.
• What the filter watches: sender authentication, domain reputation, recipient behaviour and content.
• What is at stake: emails in the junk folder or rejected outright, a damaged domain reputation and fines from the national authority.

What has changed since the article was published: The article was published in December 2015. The legal rules for commercial communications still apply, but mailbox providers have added technical requirements. Gmail and Yahoo since February 2024 and Outlook.com since May 2025 require bulk senders to have a verified domain. Gmail and Yahoo also require one click unsubscribe and a spam complaint rate below 0.3 %. We have therefore rewritten the article and added how to meet the rules in Quanda.

What spam is

Spam is an unsolicited bulk message that the recipient did not want and did not ask for. Most often it is advertising, but a newsletter is spam too if you never gave the recipient a reason to expect it. It is also called junk mail, and the folder where email programs sort it is the junk or spam folder.

The name comes from SPAM, an American brand of canned meat produced since 1937. It became famous through a 1970 Monty Python sketch in which every dish in a café contains spam and the guests are drowned out by a choir of Vikings singing "Spam, spam, spam…". A word that drowns out everything else was then adopted for annoying bulk messages. The first bulk advertising email is considered to be an invitation to a computer presentation sent in 1978 to about 400 users of the ARPANET network.

As a sender, you need to know that spam is judged from two angles today:

• Legal. A commercial communication sent without consent, without a clear sender or without a way to unsubscribe breaks the law, even if the recipient never marks it as spam.
• Technical. An email that people mark as junk in large numbers is moved to spam by mailbox providers, even if you have consent.

Only emails that pass both reach the inbox.

Why emails go to spam

A spam filter is a mailbox provider's program that evaluates every incoming message and decides whether it belongs in the inbox, in the junk folder or should be rejected outright. Gmail, Outlook.com and other providers mainly watch four things:

Source: Google, Email sender guidelines; Microsoft, requirements for high volume senders to Outlook.com; Quanda support experience.

The content of the email, once thought to be the main factor, now comes last. An email without the word "free" ends up in spam if you send it from an unverified domain to people who do not want it. And an email full of offers gets through when people want it and open it.

Rule 1: Send only to people who want your emails

A commercial communication is any message that promotes your goods, services or company. That includes offers, promotions, newsletters and webinar invitations. In the EU, sending them by email is governed by Article 13 of the ePrivacy Directive (2002/58/EC), which every member state has transposed into its own law. In Czechia, for example, it is Act No. 480/2004 Coll. on certain information society services.

You may send a commercial communication by email in two cases:

Source: Directive 2002/58/EC (ePrivacy Directive), Article 13(1) and 13(2).

In practice this means:

• Collect new contacts through a form with consent. Ideally with double opt-in, where people confirm their address by clicking a link in an email. You get provable consent and certainty that the address exists.
• Do not buy lists. You have no consent for the addresses, some of them do not exist and people who do not know you will mark you as spam. More in the article Why purchased database stinks?
• A business card is not consent. Use an address from a business card or a trade fair for a personal reply, and add it to your newsletter only after consent.

Rule 2: Verify your sending domain

SPF, DKIM and DMARC are DNS records with which the sending domain proves that the email was really sent by whoever it claims to be from. Without them, the mailbox provider cannot be sure it is not a fraudster and moves the email to spam or rejects it.

Gmail and Yahoo have required them since February 2024 and Outlook.com since May 2025. Since November 2025 Gmail rejects non compliant emails. What exactly you need:

• A company domain. Do not send bulk emails from @gmail.com or any other free email address, you cannot set up authentication on someone else's domain.
• SPF and DKIM. In Quanda you set them up with three CNAME records found in Settings / Domain & DNS verification. The procedure is described in the guide DKIM, SPF, DMARC, link branding and sending domain verification.
• DMARC. A TXT record with your domain's DNS provider, the p=none policy is enough to start with.

You will find a detailed step by step procedure and an overview of all requirements in the article Gmail, Yahoo and Outlook requirements for bulk email senders.

Rule 3: Label every email, sign it and make unsubscribing easy

EU law sets three requirements for every email with a commercial communication:

1. it must be clearly identifiable as a commercial communication,
2. it must not disguise or conceal the identity of the sender on whose behalf it is sent,
3. it must contain a valid address to which the recipient can send a request to stop such communications.

Source: Directive 2000/31/EC (e-Commerce Directive), Article 6; Directive 2002/58/EC (ePrivacy Directive), Article 13(4).

What this means for every email you send:

• Label. Make it clear that the email is a commercial communication, for example in the footer next to the sender details. Some countries, such as Czechia, require this label explicitly.
• Sender. Both the sender name and the address must make it clear who is sending the email. Put your company name and contact details in the footer.
• Unsubscribe. Keep the unsubscribe link clearly visible. A hidden link does not only break the law, people who cannot find it click Report spam instead.

In Quanda, the unsubscribe link is part of every email campaign. When a recipient clicks it, Quanda immediately removes them from further mailings. Do not delete unsubscribed contacts, otherwise the information about the unsubscription is lost and you could import the contact again by mistake. More in the guide Unsubscribed contacts.

Tip: Unsubscribing is not a defeat. A person who unsubscribes does not damage your reputation. A person who cannot find the unsubscribe link and marks the email as spam does. Why an unsubscription is better than a complaint is explained in the article Email open rate: is 20 % a lot or a little?

Rule 4: Send content people open and clean your list

The spam complaint rate is the share of recipients who marked your email as junk out of those to whose inbox it was delivered. Google requires keeping it below 0.3 % and recommends below 0.1 %. That is one complaint per thousand delivered emails. Campaigns sent from Quanda have stayed below 0.03 % over the last 36 months (October 2023 to September 2026), ten times below the 0.3 % limit Google requires and more than three times below the recommended 0.1 %. You can watch the spam rate for Gmail in Google Postmaster Tools.

To keep complaints as low as possible and your sender reputation as good as possible:

• Send regularly. Avoid big swings in the number of emails sent during a week and a month. A company that sends 20,000 emails once a year looks like a spammer.
• Send value, not just "buy now". A guide, a tip, news that helps the reader. When all you send is discounts, people stop opening your emails and start marking them as spam.
• Remove invalid addresses. Quanda automatically moves addresses that an email could not be delivered to into blacklisted contacts and does not send further emails to them.
• Remove inactive contacts. People who have not opened your emails for a long time worsen your sender reputation. In Quanda you can find them with contact scoring by open rate. Remove the Ghosts category, contacts with no open and no click in the last 12 months, from regular mailings completely. Send only occasionally to the Zombies category, with an open rate below 5 % in the last 12 months. Watch the scoring continuously and send re-engagement campaigns to inactive contacts.
• Run the spam test before sending. In the campaign's sending settings, Quanda tests the email both technically and for content. The result is a number from 0 to 10. An email scoring below 10 can technically be sent, but the criteria of Quanda's test are stricter than usual and we recommend staying as close to zero as possible. The procedure is in the guide Setting up mailing in a simple campaign.

The most common content mistakes the spam test reveals:

• a subject line written in capital letters only or full of exclamation marks,
• an email made of one large image without text,
• links hidden behind URL shorteners,
• a missing text part and unsubscribe link.

How to write a subject line people open and filters let through is described in the article How to write an email subject line people actually open.

How to find out whether your emails go to spam

Nobody reports spam to you. The recipient simply never sees the email in the junk folder. That is why you should watch these signals:

1. The spam test before sending. A result close to zero means the technical side and the content are fine.
2. A test email to several mailboxes. Send the campaign to Gmail and Outlook and check which folder it arrived in.
3. Campaign statistics. In Quanda's statistics you see the number of recipients who marked the email as spam and their list. The meaning of all the numbers is explained in the guide What the terms in statistics mean.
4. A sudden drop in open rate. When a campaign's open rate drops sharply compared to previous ones for no obvious reason, part of the emails probably ended up in spam.
5. Google Postmaster Tools. It shows the spam complaint rate, domain reputation and delivery errors to Gmail.

If the email did not reach the mailbox at all, the article Reasons for undelivered emails explains the error codes from 421 to 554.

Checklist: an email that stays out of spam

• I send only to contacts with consent or to existing customers.
• I collect new contacts through a form with double opt-in.
• I send from an address on my company domain, not from a free email address.
• My domain has verified SPF, DKIM and a DMARC record.
• The email is identifiable as a commercial communication and the footer contains the company name and contact details.
• The unsubscribe link is clearly visible.
• The spam test in Quanda is close to zero.
• The spam complaint rate is below 0.3 %, ideally below 0.1 %.
• I remove invalid contacts and the Ghosts category and send only occasionally to Zombies.

Conclusion: spam is what people do not want

Spam is not about a single word in the subject line. It is an email the recipient did not want. When you send to people who gave you consent, from a verified domain, with a clear sender and unsubscribe and with content that interests them, you will reach the inbox.

The online course Email Deliverability from A to Z explains deliverability from domain verification to metrics. If you are not sure what to do, write to us at support@onquanda.com or call +420 605 163 892. We will also be happy to go through your settings with you in a free consultation.

I am keeping my fingers crossed for you!