Keep e-mails out of spam

Estimated reading time: 3 min


Whenever you send an e-mail, you want it to be read by the recipient. Your recipient probably has spam filters on his mailbox, which may be triggered due to misconfiguration or error on your own mailserver. This is how you keep e-mails out of spam.

This article explains best practices for deliverability of outgoing mail.

The sender

Your “From:” address should be a working e-mail address. Some mailservers require the existence of the “From:” address but even if this is not required you should use an existing e-mail address so you can receive any delivery errors (bounces).

The recipient

On many occasions we have seen that recipients not mentioned in the “To:” address end up in the spam folder at the recipient. If your recipient is mentioned in the CC or BCC, try sending your e-mail again, directly mentioning the recipient in the “To:” address.

The subject

The subject line might not be the first thing a spam filter evaluates, however it actually is the most important thing recipients look at when they report an e-mail as spam. By doing this, you train your spam filter to recognize similar emails as spam too. This is why choosing the right subject, is important. When choosing a subject, keep in mind: What would my first impression be, if I were to receive this e-mail? If the answer is “this is spam” or “this might be spam” choose another subject.

The content

Spam filters will evaluate the body (content) of your mail. Try to avoid “spammy” words. Also, make sure your mail contains enough text. Example: When you send an invoice to your recipient, your e-mail body  should contain more words than “See attachment”.


Speaking of attachments: We have seen on many occasions, that an e-mail without an attachment is delivered correctly to the Inbox. The same e-mail, with same sender, recipient, subject and even the same content, might end up in the spam folder, with the addition of a single attachment. Try sending your mail without an attachment.

Authentication, i.e. SPF, DKIM and DMARC

Last but not least: make sure your SPF records, DKIM records and DMARC records are created correctly and authorize the mailserver sending the mail on your behalf. This, to make sure that others can determine whether you should be allowed to send mail on behalf of the domain of the sender.


Avoid using mailservers which are listed on a blacklist. Also avoid linking, or mentioning domains in your mail which are blacklisted.

How to verify whether your mail is “good”

This is complicated right? It is even more complicated to verify whether your mail actually adheres to these best practices.

Fortunately, there is an easy way to “Test the Spammy-ness of your Emails”:

Make sure you send your e-mail to, the exact same way, with the exact same content. The only difference should be that the e-mail address should be mentioned as a To: address (it won’t work in CC or BCC!).

The results should help you to improve the your message.

I have followed up on all pointers and I’m scoring a 10/10, but my mail still ends up in the spam folder. What more can I do?

Unfortunately this does happen. While this article certainly helps with deliverability issues, it is not an exhaustive list of factors that could send off your mail to the spam folder. The issue may lie on the receiving end. The recipient may have trained his personal spam filter by triggering it with too many e-mails with content similar to spam. Another issue may be an overly restrictive or an otherwise malfunctioning spam filter.

When you’ve followed the recommendations in this article and your score on is near perfect, the next step is; Evaluate why your mail is marked as spam. Unfortunately this information is only available to the server administrator of the recipient. The only way to receive this insight, is by having your recipient ask this to his / her mail provider. It is important to have the following information ready:

  • What was the ‘from’ address (sender)
  • What was the ‘to’ address (recipient)
  • What was the ‘subject’
  • When was the mail sent (date, time and timezone)


With the help of this article you will be able to get your mail delivered to the Inbox of your recipient. In the unfortunate case where the mail still ends up in the Spam folder, you’ll have the information to debug this.

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