Email content best practices

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Creating good email content increases the general success of the ability to maintain good inbox placement. ISPs protect their users by using spam content filters, which work by analyzing a message before it is sent to the recipient’s inbox.

Spam filters are used by ISPs to score incoming messages based on algorithms that find thousands of characteristics, misspellings, the similarity of words that occasionally show up within the spam folder. Legitimate emails can end up into the spam folder if their messaging contains any similar characteristics or commonly used tactics by spammers.

Refining your content to industry standards will allow you to stand a more robust chance of reaching the inbox.

This topic describes how content affects your email deliverability and provides insights into how you can improve your content strategy. Following some best practices can facilitate a successful email campaign, some smart rules include:

HTML syntax errors

Using out-of-date or invalid code will influence if your emails are accepted by domains like Hotmail, Gmail and AOL are blocked or delivered to the spam folders.

Your finished email might render well among these ISPs but if the hypertext mark-up language email doesn’t comply with W3C standards (World Wide Web Consortium) you may find deliverability problems. HTML syntax and formatting errors are common tricks spammers use to get past content filters.

Text image ratio

ISPs often block emails that contain only images as a means to fight against spam. Image only emails have been known to have higher abuse complaints, higher bounces, lower email engagement. The most common used guideline is no more than 40% image and a minimum of 60% text.

Unsubscribe link

Including an unsubscribe link within your email is a fundamental rule for email marketing. The unsubscribe link should be clearly visible, with a one or two click process, allowing the recipient to remove themselves from the database instantly. If a recipient is unable to find your unsubscribe link, they are more likely to click the “this is spam” button, which can lead a mark being left on your sender reputation.

Privacy policy page and imprint URL

A privacy policy is a legal requirement for all websites that collect or use personal information from users. Adding a privacy policy link to the intended recipient destination shows ISPs that you are a sender that complies with regulatory guidelines.

Adding an imprint to your email template maintains transparency, it is recommended to include name of the authorized sender, email address, phone number, postal address and business registration number to the footer of your emails.

Image: Example email footer


Adding email attachments as a bulk sender are prohibited, doing so will flag your emails as spam. Attachments are often used to hide malware and viruses. ISP tend to block emails containing attachments to protect recipients and infrastructure.

Avoid spammy words and phrases

ISPs have become smarter about how they distinguish a spam email from a legitimate email by scanning spam words and phrases. As an email marketer doing adequate testing before a send and removing common spam words from your copy such as Click here! or Free can assist in better inbox placement. A good way of knowing what to exclude is to review the content within your personal spam folder.

An example of spammy content include:

  • Excessive use of exclamation points
  • Dear Friend
  • Order Now, Risk-Free
  • Discount
  • Offer
  • Sale, Buy, Free, Cheap
  • Keep the following signs to a minimum: ?, %, $
  • Exclude the use of ALL CAPS
  • The use of bright red/green colored fonts

Link shorteners

Link shorteners are appealing since they make your links more manageable, but in reality, using such tools increases the chance of your emails being flagged as spam. The reason behind this is that link shorteners mask your destination URL, this technique is often used by spammers to prevent recipients and the ISPs from knowing your actual website domain.

Avoid mismatched URLs

Mismatched URLs are a clear sign of a phishing attempt, avoid looking like a phisher by removing unintentionally mismatched URLs. This occurs when the link text is a URL and does not match the URL in the link HREF that the recipient is directed to.

Remove blocked URLs

Domains listed on blocklists should not be used. If it is a client’s domain, then the client should investigate with his domain host. If it is a third-party domain the client links to (for example, it should not be used anymore due to a bad reputation.

Plain text version

There are many good reasons to include a text version of an email, in the event that HTML version is not accepted or cannot be rendered, the message will still be able to be displayed in text format. Text versions should be identical with the HTML version in terms text content and links.

Domain alignment

All domains that you use for sending, tracking or in e-mail content should be aligned. You can set up the alignment in relaxed or strict mode. Both modes are accepted throughout the industry and prevent emails from being classified as spam or phishing attempts by spam filters and at the same time create more trust on the recipient side.

With relaxed domain alignment, the domains used must be the same, at least at the organizational domain level. Example for relaxed domain alignment:

Visible sender domain Technical return path domain Tracking/image domain Domain in email content

With strict domain alignment, the domains must also be aligned at the subdomain level. Example for strict domain alignment:

Visible sender domain Technical return path domain Tracking/image domain Domain in email content

Using similar but not the same domains, such as or, is strongly discouraged. For a spam filter, these give the impression that they are part of a spamming or phishing campaign and can harm delivery.

Bad content creates low engagement

The messaging within your emails also influences your inbox placement, it is essential to ensure that you are sending email content that your recipients want to read. ISPs will analyze how engaged your recipients are by looking at opens, clicks, bounce rates, unsubscribes, and spam complaints. Low-performing emails are usually sent to the spam folder. Good practices to keep your recipients engaged include providing personalizing content based on your recipient’s needs, adding CTA points, keeping subject lines short, content messaging less salesy, segments, personalization, and dynamic content.

A/B testing is an important technique that can help you understand, how your recipients respond to different content, and which campaigns are most effective with engagement metrics.

Other recommendations

  • An email message size should be less than 200 KB in general. Redundant code, increased image sizes, and template height /width can influence the overall size of your email. (Email size to Gmail should be a maximum of 102 KB.)
  • The subject line should have a maximum length of 50-60 characters.
  • Add a comment to your emails, requesting your recipients to add your email address to their safe senders list.
  • Remove any iframes from your templates.

In conclusion, we have seen that content influences not only the value to your recipients but following the above tips, improves your ability to gain better inbox placement and a better-performing sender reputation as ISPs start to trust you as a bulk sender.