Email marketing deliverability: tips to circumvent spam filters

Emails, even with valid email addresses, often never reach the recipient’s inbox. Deliverability is a big issue for most email marketers. The percentage of emails that get stuck in spam filters, the filters of ISPs and other filters, varies. 

It depends of the quality of your email list, the number of email adresses and several other factors. 

According to an older study by Assurance Systems, on average 15% of all emails with a valid email address never reach the recipient. Knowing that every year more emails are sent, the struggle to reach the inbox becomes tougher.

Is email marketing then no longer effective or will it become less effective? No! It will remain effective if you keep it relevant, and if you follow the rules. 

There are many techniques for filtering spam that can be applied at different levels (PCs, e-mail servers, ISPs, etc …). Here are some tips to avoid that your emails get blocked by spam filters. 

1. Select a technical partner who is familiar with the problem of spam and has the right technology available. It is very difficult for you as a marketer to control all technical aspects of spam filters. 

2. If you use your own infrastructure for your email campaigns, first make sure your infrastructure is not included in a spam database. You can check this via

3. Apply the KISS principle: keep your emails as simple as possible. Avoid using capital letters and bright colors. A colored background ensures a higher spam score. Don’t get all flashy. If you use rich media or video, make sure that you work with an ESP or other partner that provides the tools you need to include them the right way.

4. Check the content of your mails on typical spam features. Try to avoid as much as possible words such as “free”, “cash”, “bonus” etc. There are several tools that are used for e-mail spam filtering based on content-matching rules. You can use them yourself to see how they work. Normally, your ESP should also be able to provide you a tool or at least a list to check the content (and even your email as such) in order to avoid getting blocked.   

5. Manage your lists carefully. Of course you always ask permission prior to sending an email. Use double opt-in subscription where possible. Tell new subscribers from where the email will be sent and ask them to add it to their trusted senders list of their spam filter. Keep your lists up-to-date. Remove email addresses that don’t exist anymore and look at your bounces.

6. Keep it relevant. Should I even repeat this? You can read about the importance of relevance in email marketing everywhere in this blog. And, as I wrote earlier, it’s possible that pure filtering based on content, might be replaced by criteria such as open rates, CTR, etc. in the future by ISPs. And what defines how many people interact with your emails? Right, relevance!

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