Improve Email Deliverability

What Causes Spam?

An email can be marked as spam for a number of reasons. Some of these are because of the recipient’s email server settings, the others are due to the types of content contained in the sent email. The following are some examples of email contents that could hinder deliverability and potentially cause an email to be marked as spam.

Note: The following tips and suggestions can help improve deliverability, but are not a guarantee of delivery or spam prevention. It is always suggested that you get approval to email a client or lead by sending an opt-in request.


What Spam Filters Look For

It is common practice for Internet Service Providers (ISPs) to protect their users with the help of spam filters. Using the wrong words or even characters in your email can trigger the spam filters and therefore throw your email into the spam folder.

The key thing to remember is that a spam filter is trying to remove commercial advertisements and promotions. Generally, words that are common in such emails should be avoided or used sparingly.


Email Subject Trigger Words

Spam filters can be triggered for a variety of reasons, causing your email to skip recipients’ inboxes and land straight in their spam folder. Words in an email subject line that can trigger an email to go to a spam folder are known as trigger words. Avoiding these words in your email subject lines can dramatically increase your chances of getting beyond spam filters.

Examples of trigger words to avoid: free, affordable, discount, cheap, best price, cost, quote, save up to, call now.


High Complaint Rate

If too many people are marking your email as spam, ISPs will take action and start sending your email straight to the spam folder. After that, they may start throttling your messages or even block them. Keeping an eye on the complaint rate is critical if you want to reach the Inbox.


No Unsubscribe link

It is important to give your clients the choice to opt-out of a emails and communication; this is known as an unsubscribe link. Not adding an unsubscribe link to emails will force a subscriber to hit the spam button in order to stop receiving emails. Some studies have shown that you can lower complaint rates by simply placing the Unsubscribe Link at the top of your emails because this makes it more visible and easy to find.

Note: Service Autopilot adds an Unsubscribe link to all Marketing and Automation emails.


High Frequency

The number one reason subscribers hit the spam or unsubscribe buttons in an email is due to receiving too many emails. ISPs want to make sure that their users’ mailboxes don’t get crowded. In order to protect their users from email fatigue, they can start junking the messages. To avoid this, it is important to include an Unsubscribe Link in your emails. This lets your subscribers tell you how often they want to hear from you.


Sending to Inactive Users

Subscribers often lose interest and stop opening emails over time. A common response for senders is to then send emails to more users. However, this will hurt your deliverability even more because ISPs have ways of monitoring the activity of the users. ISPs can check whether users open emails, click links, delete emails, or mark emails as spam. Basically, they monitor the users’ level of responsiveness or engagement. Based on these metrics, ISPs decide whether the email goes to the inbox or spam.



It is important that your company's domain name has HTTPS. The “S” stands for secure. More specifically, your HTTP request is using Secure Sockets Layer (SSL). SSL is a protocol used to secure communications between a client and server. The protocol employs encryption to keep eavesdroppers from “hearing” your conversation. It also keeps a hacker from hijacking your conversation, feeding you false information, and gathering information from you that you assume is protected. You can tell your domain is secure if the URL has a small lock and "https" before the "www." 


Rejected Email

An email displays as Rejected when it’s removed from your outgoing list before it is sent. Reasons for rejection include:

  • Opt-Outs - The person to whom you are attempting to send an email has requested not to receive Marketing or other notifications via email. They might have clicked an opt-out link, or you might have tagged that client as “Do Not Market.”
  • Invalid Address Formats - When sending an email to an invalid email address, it will be marked as bounced first. This would catch things like “fish@motorcycle” because valid email formats need to end with dot-something.


More information on SPAM Triggers

Here is a list of words and phrases to watch out for when creating Marketing emails from a Hubspot article: 100 Spam Trigger Words & Phrases to Avoid.


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