10 rules to follow to avoid email being marked as SPAM

1. Send commercial communications only to recipients who have given their consent

You may only send commercial communications to contacts who have given you permission to do so. You have their verified and verifiable consent, called double opt-in. Or they are your customers.

Do not send email marketing communications to contacts who have not given their consent or have opted out of receiving these marketing communications. This is illegal, and it does not give your customers a good image of your company. In addition, a well-maintained database will keep your customers happy, especially since you will only send communications to contacts who are interested. If you don't do this and send your communication to contacts who are not interested, they may mark the communication as spam and you will then have a problem reaching customers who are interested in your business communication. This saves you time, money and allows you to target those users who bring you profits. They are important to you.

2. There must be a link in the email to easily unsubscribe from correspondence

The recipient must be able to easily unsubscribe from the communication they receive via a link in the communication. This request must be processed immediately and no further commercial communications may be delivered to that user.

The recipient has the legal right to unsubscribe from email communications. Please note that you should never hide this link and make it impossible for the recipient to do so.

Options on how to unsubscribe from the user:

By clicking on the unsubscribe link in the body of the email.
By clicking on the unsubscribe link located in the header of the email client.
Click on the SPAM link.
Unsubscribing people who have a long-term undeliverable mailbox.
Unsubscribing people who have a repeatedly undeliverable inbox.
Manually handling responses to outgoing emails - reply with a request with removal from the database.
Synchronisation with other corporate systems and updating data.

3. The sender must provide his/her identification data.

By law, the sender is required to identify themselves in the body of the message with their company name, ID number and contact information. The address used for sending and receiving responses must be fully functional. Please note here that a non-functional email address must not be used for sending. It is also undesirable to use addresses from freemail services (Seznam.cz, Centrum.cz, Gmail.com, ...).

Sending from a freemail address leads to automatic penalties from antispam filters. Definitely set up your own domain for your business or use it for emails. Only with your own domain can you have control and prevent abuse of your brand. At the same time, to meet the technical requirements of email providers (Gmail.com, Seznam.cz, Centrum.cz, ...), your own domain is a must. The form of domain protection has an increasing influence on the deliverability of email messages.

4. Email must meet the technical requirements of current standards

In order to avoid ending up in SPAM, your e-mail message should meet certain technical requirements. Both according to current standards and recommendations. DKIM signature, valid SPF, correct letter - unsubscribe headers and FBL registration are the basis.


SPF is one of the technologies that protects message senders from name misuse and spamming on their behalf. It is a record that defines a list of IP addresses. They are authorized to send messages on behalf of a domain. However, this technology has its limitations. It verifies the sender's address according to the technical envelope of email communication called MFROM. But not FROM, which means the sender's visible address. As a result, this can unfortunately mean that SPF cannot prevent emails from being sent from a subject who is impersonating a foreign sender.


DKIM technology is another security factor in email communication. It is the digital signature of email messages. It makes it possible to verify that the content of a message has not been changed after it has been sent. With the help of this technology, it is easy to trace who is responsible for the message sent, who sent it. This specific responsibility of the DKIM signature then also means that the reputation can be linked to specific keys and domains.

Double DKIM signatures are also gradually becoming standard. An e-mail message is thus signed not only with the sender's key, but also with the e-mailing solution provider's key.


DMARC builds on existing DKIM and SPF technologies. It is constantly expanding and linking their individual destinations. It allows the domain owner to monitor the email flows of his domain and thus detect possible misconfigurations, security risks and protect against third-party attacks.

DMARC is bound to the sender's domain, which is visible in email clients. This makes it possible to protect against e.g. phishing attacks. Currently, this is the highest level of protection for email communication.

These technologies not only protect the sender and the brand, but also prevent the delivery of fake emails aimed at fraudulently obtaining sensitive data from recipients.

5. The subject must not be written in CAPITAL LETTERS

The subject line of the email itself also plays a big role. It must not be in capital letters. It must contain clear information about what the user will find in the body of the email itself and must not be confusing. Try not to insert special characters (e.g. emoji) and be concise.

In short, the subject line deserves a lot of attention and is the main thing that will entice the user to open the email.

Avoid using capitalization, question marks and exclamation points in the same subject line (Looking for? You'll find us!). This is more likely to distract the recipient and make them feel like you are shouting at them. You may also get penalised by anti-spam filters.

Don't forget the pre-header either. This is the first sentence of the email message that appears right after the subject line and is about 80 characters long. So you have another 80 characters to entice people to open your message.

6. The message must be clear, understandable and truthful

The content of the email message must be easy to understand, truthful and deliver value to the recipient. The body text must be as legible as possible without the need to load images. In the case of commercial messages, the wrong step is when you use an embedded attachment, in any format. This only ever links to the files from the email.

Follow a simple rule here. Only prepare and send emails that you yourself enjoy and would like to receive. So forget about the austere email in which you link to an attached file. A text like "Hello, everything is attached to this communication in pdf" may not be delivered to the recipient at all due to mail client limits and is worth absolutely nothing.

Only include what is true in the email message. Don't lie because it will always backfire sooner or later.

At the same time, don't forget to use alternative captions for images, which are shown to the recipient after they are loaded. Then be sparing with images, because everything must work without them. This is mainly because email receiving applications are blocked from displaying images by default. This is also because many email services penalise email messages that are purely made up of images.

One last thing. If you want to sell something and you put a unique offer in an image that the customer can't see. Do you think that will have an effect?

7. The links in the email must be functional and clickable

Links in an email need to be clickable and functional. They cannot be presented in text form.

In short, include links in the email message that are live and valid. None of your recipients will want to copy a text link and paste it into a web browser.

8. The frequency of messaging should respect the recipient's interests

Only send emails when you have something to say. Regularly monitor how users react to your mailings and act accordingly. Some people will be happy with a newsletter delivered twice a week, others once a month. However, remember that the basic rule of thumb is to send one email message at least 1x every 90 days. This will let you know if email inboxes exist in your database and then continually remove the non-existent ones. This will give you an up-to-date database of contacts. At the same time, make sure that your customer is in certain buying cycles. Adjust the frequency of sending and the type of communication accordingly.

9. Keep your database up to date

Remove non-functioning recipient addresses regularly. Only in case of temporary limitations (e.g. the recipient's email inbox is overflowing), you can resend. Then remove unavailable addresses from your database completely.

We classify undelivered emails into two categories

Temporarily undelivered (soft bounce) - you cannot receive email messages temporarily. For example, due to a full mailbox.
Permanently undelivered (hard bounce) - you cannot receive email messages permanently because the mailbox does not exist.
Why do you need to clean the database?

Email services evaluate the frequency of attempts to deliver email messages. Undeliverable addresses then determine the reputation of the sender itself. And for email services, this is a clear identifier that the sender is not following proper emailing policies or is a spammer. He does not care about cleaning the database and his goal is to send as many messages as possible.

At the same time, we also recommend removing non-responsive recipients from your regular email campaigns in case the reactivation campaign doesn't work either. This is because antispam filters take recipient reactions and reputation as one of the most important signals. Therefore, campaigns that have a low open rate are more penalized and thus more likely to fall into SPAM.

10. Look after your beneficiaries

Think of email marketing as one of the leading tools that strengthens your relationship with your customer. Nurture it properly and it will pay you back many times over.

The message you send in this way must have some benefit and added value for the recipient. Not just for you and your business and marketing goals.

Your customers are smart and know very well what they want. They are not waiting for anything amazing, so the biggest mistake marketers make is to disengage from any respect and interest from the recipient.