How to avoid spam filters

Spam (also known as junk email) are unsolicited messages usually sent to a large number of users to spread malware, advertise, or scam the recipients.

Email service providers (ESPs) analyze and filter out such messages using sophisticated algorithms and formulas. To make sure your legitimate emails don’t get labeled and land in the Spam folder, you can use the following guidelines:

Use only a dedicated IP address

Your sender reputation might be too low to send campaigns when a dynamic IP is used to send emails. This happens because you are not the only person sending from this IP, meaning you can not be in full control of your sender reputation. Sender reputation is one of the main parameters used by spam filters to determine spam emails. 

Always check your IP reputation

We recommend you check it using Talos Intelligence. You can also use Sender Score for more detailed IP reports. 

Check email lists for outbound campaigns for validity

To save your IP reputation from getting damaged by a large number of bounces from invalid emails, make sure you always verify emails. Ignoring this step might lower your sender reputation and result in more emails being marked as spam. 

Follow your email campaign statistics to determine the campaign’s effect on sender reputation

As statistics like open rate and spam complaint rate affect your sender reputation, we recommend that you monitor your campaign statistics and edit campaigns if you notice any of the emails showing performing poorly. You can always use the average rates statistics for comparison:
– an average open rate is 20.81% for B2C and 15.1% for B2B;
– the unsubscribe and spam complaint rates should be no higher than 0.5%;
– the bounce rate should be less than 2%. 

Warm up new email accounts

Before sending large email campaigns (more than 500 recipients), warm up the new email account with smaller campaigns to preserve the sender’s reputation and make new accounts look less suspicious to the ESPs. 

Create a separate domain name and email account for outbound marketing

Ideally, all your email campaigns should be sent from separate SMTP accounts to not affect each other’s deliverability, so send all your emails – outbound, transactional, marketing, newsletters, etc. – from dedicated SMTP accounts. This way you’ll be 100% confident in your sender reputation. 

Set up SPF, DKIM, and DMARC records

This will help you make sure the emails you send are allowed to reach the inboxes of the recipients and save your data from phishers and hackers.
Learn how to create an SPF record for your domain here.
Read how to set up DKIM here.
Read how to set up DMARC here

Avoid using spam words in the subject line and email body

Spam trigger words in the subject line and the email itself will trigger spam filters and the emails will likely end up in the Spam folder. 

Send plain-text emails and minimize HTML ones

While HTML-heavy emails will not necessarily end up in the spam folder, they are extremely likely to land into the Promotions folder instead of the main inbox. If you want to avoid this, you may want to switch to plain-text emails. 

Do not use too many pictures

Spammers are notorious for using pictures instead of text to bypass the spam trigger word checks. ESPs fight this by analyzing emails’ text-to-picture ratio. Keep the text-to-picture ratio at 80-to-20 to stay safe. 

Add custom variables to emails

Sending absolutely identical emails to different recipients will trigger the spam filters. Adding personalization will help avoid this problem and add a human touch to your emails. 

Don’t use multiple colors, fonts, and capitalized words

Excessive formatting is another thing spammers are known to do, meaning ESPs are already on the lookout for this and the spam filters might mark your email if you use multiple colors, fonts, or too many capitalized words. 

Don’t overuse attachments

Multiple or heavy attachments are beloved by spammers, so spam filters analyze them especially meticulously. This decreases email deliverability. 

Spam test your emails

Use special spam testing tools to see if your email will pass through all the spam filters, for example, GlockApps

Observe sending behavior best practices

This includes:
– don’t send through open relays
– attach an unsubscribe link
– don’t send to purchased email lists
– include the true header
– send emails that are at least one sentence long 

Stick to the ESPs email sending limits

Otherwise schedules emails simply won’t reach the recipients. 

Don’t send messages to generic corporate email addresses

Emails sent to generic emails like,, etc. simply won’t be opened. Open rate can also affect your sender’s reputation. 

Don’t track links unless necessary

Link tracking can hurt your email deliverability. 

Keeping these requirements in mind will help you avoid ESPs spam filters. However, your sender reputation can also depend on the recipients’ reaction to your emails. Read what pushes people to mark emails as spam here.

Learn more tips on how to avoid spam filters and make sure your emails always land in the Inbox in our video:

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