Sender Reputation: Your Role in Improving Your Deliverability

Inside ConvertKit
12 min read

Hi! My name is Alyssa Dulin and I’m the Deliverability Lead here at ConvertKit. Before we dive into what my role entails, let’s define deliverability.

There are two terms that are often used interchangeably, but actually have different meanings: delivery and deliverability. To understand the difference, we’ll need to first touch on how email sending works.

The process of sending an email happens through a back and forth conversation between servers that looks sort of like this:

The process of sending an email between sender and receiver

In the illustration above, the receiver is the subscriber's mailbox provider – MBP (i.e. Gmail, Hotmail, Yahoo, etc.). Notice, at the end of the conversation, the sender confirms message acceptance. At any point in the conversation, the message could bounce. The mailbox provider would let the sender know that the message was not delivered.

This process is referred to as delivery. Delivery rate is different and refers to number of emails successfully delivered divided by the number of emails sent. The great part about delivery is that it can be very easily measured!

ConvertKit maintains a system-wide delivery rate of over 99%. Later in this post, I’ll talk more about what ConvertKit does to maintain a healthy delivery rate.

Once a message has been successfully delivered, it’s now in the hands of the MBP which can place the email in the inbox, spam folder, trash, or even just drop it into thin air. Each MBP has its own unique algorithms and freedom to handle an email however they’d like.

Deliverability is the measure of your messages’ inbox placement. The goal for all senders is to have good deliverability, which means lots of messages are being placed in the inbox.

With delivery, it’s really easy to measure performance. A message was either delivered or it wasn’t! Unfortunately when it comes to deliverability, it isn’t as straightforward to measure success.

MBPs do not tell the sender what happened to the message after it was delivered. Only the mailbox provider and the subscriber will know where the message was placed after delivery happened. This means we mostly focus on open rates, click rates, and conversion rates to indicate the performance of a sender’s deliverability.

There are numerous factors that will dictate whether a message is placed in the inbox or the spam folder. Some factors are influenced by ConvertKit, but most factors are influenced by the message’s sender.

ConvertKit’s role in deliverability

ConvertKit provides the IP addresses, sending domains, and link tracking domains for your messages. Each of these items carries a reputation and my job, along with our Compliance Lead and Deliverability Engineers, is to ensure that all of these components have a healthy reputation, influencing MBPs to place your message in the inbox.

One great way to measure the health of these items is by looking at ConvertKit’s system-wide delivery rate. As mentioned above, ConvertKit maintains a delivery rate of at least 99%. I’ll be publishing monthly deliverability reports to provide you with more detail about our deliverability health.

Along with keeping the reputation of our infrastructure healthy, we also:

  • Ensure that messages are being sent at the proper rate for each mailbox provider
  • Stay on top of industry news and trends, adapting to any changes
  • Maintain relationships in the email industry so we can advocate for our customers
  • Stop spammers from using our platform maliciously
  • Manage feedback loops to ensure subscribers who complain are inactive from your list, and let you know if your complaint rate becomes elevated
  • Handle bounces to ensure that invalid addresses are inactive on your list and don’t harm your reputation

Sender reputation: Your role in deliverability

While ConvertKit helps your messages get through the door, most of the factors that influence deliverability are in the hands of the sender. The top components are:

  • list collection
  • list health
  • sending frequency
  • content

These ingredients determine how engaged your subscribers will be, and the way that your subscribers engage or don’t engage with your emails will determine your sender reputation. The domain you’re using to send messages carries its own reputation and this has the biggest influence on inbox placement.

To have a good sender reputation, you’ll want to send as many positive signals to MBPs as you can and minimize any negative signals. These signals are sent by the way your subscribers interact with your messages. The chart below indicates which subscriber actions are positive, neutral, or negative.

How a subscriber responders to your email affects your sender reputation.
How a subscriber responds to your email affects your sender reputation.

List collection

Only import subscribers who have given you direct permission to receive email marketing. Quality is much more important than quantity when it comes to your list. You don’t want anyone on your list who doesn’t want to be there.

The quickest way to receive complaints (when subscribers mark your message as spam) is to send emails to subscribers who didn’t opt-in to receive your messages.


For the best deliverability, be sure everyone on your list knows exactly what they are signing up for. Collecting subscribers through a form or landing page with double opt-in enabled is a great way to ensure your subscribers want to receive your emails.

List health

The permission we talked about above doesn’t last forever. After building a list of subscribers who want to receive your messages, be sure to clean up the list often.

Another big detractor to deliverability is when a sender continues to send messages to subscribers who have been unengaged.


I’d recommend setting up an automated re-engagement sequence so that when a subscriber becomes cold, they begin receiving re-engagement messages. If the subscriber is still cold at the end of the sequence, it’s best to remove them from your list.

Sending frequency

Be sure that you’re sending emails as frequently as your subscribers want to receive them. Some subscribers might love daily emails while others might prefer weekly or monthly. Another reason subscribers often mark messages as spam is if they are receiving them too frequently.


Don’t be afraid to ask your subscribers for their preference. Send a quick survey to find out how often they want to hear from you.


Similarly to frequency, personalization is key. Make sure your content provides value to your subscribers.

To do this, it needs to be relevant to them. It’s always a good idea to learn more about the type of content your subscribers want to receive from you and send accordingly!


Our tagging feature makes this easy to implement. And other than personalization and relevance, here are some technical guidelines to keep in mind when building the content of your message:

  • Aim for at least 500 characters: Too little text can be a red flag for spam filters.
  • Don't Use Link Shorteners: Because link shorteners are used so often by spammers, they can raise a red flag for spam filters. Transparency is key for good deliverability. When adding a link to your emails, link directly to the website you're sending subscribers to.
  • Spammy words and phrases: One of the biggest mistakes marketers make is using language that’s overly promotional and/or urgent. Even if you are selling something in your email, try to write your email so that it sounds human and conversational.

Words not to use in sales emails subject lines

  • Image-to-text ratio: There’s no magic number here, but the best guideline to follow is to have enough text in your email so that if images failed to load, you’d still have a great email that communicates your message.
  • Avoid gimmicks: While you might see a quick boost in open rates from a subject line that says “Re: Your Order #2095642”, you’ll lose subscribers’ trust. Your audience will be much more likely to mark the message as spam or become disengaged with your emails. Avoid quick tricks to boost engagement.
  • Encourage authentic engagement: Give your subscribers permission to engage with you in an authentic way. This engagement will help boost your sender reputation but also help build a relationship with your subscribers. For example, if your email is about coffee brewing methods, ask your subscribers to reply to your message with their favorite home brew method or one they are excited to try next.

How to check your sender reputation

While sender reputation is similar to a credit score in many ways, one major difference is that you can’t determine a concrete score for your sender reputation. Each of the mailbox providers has a unique score they’ve determined for you, and they keep this information private. If they made sender reputation data public, it could be used by spammers to game the system. The best way to assess your sender reputation is through your engagement metrics.

Open Rate

Here are the open rate ranges and how they can inform you of your sender reputation:

           Open Rate         

Likely Sender Reputation

0% – 9%


10% – 19%


20% – 29%



Very High

However, the correlation between open rate and sender reputation isn’t always this simple. For example, you could have a great sender reputation but have an authentication failure and see very low open rates. It’s important to check out the 7 action items below so you can check for other factors.

Open rates are also not always accurate.

There is a small tracking pixel in every ConvertKit message. When the pixel is loaded, an “open” is triggered. Most of the time, the pixel is loaded because the subscriber actually opened the message. However, this pixel can be loaded for other reasons as well, making open rates not 100% accurate all of the time. For example, if a subscriber is using a strict spam filter, it can cause all images in the email to be loaded automatically regardless of whether the subscriber actually opened the email.

Click Rate

Click rate is much more individualized to your content and strategy. The most important thing is to keep an eye on your click rate and notice any major drops or improvements and adjust accordingly. A drop could signal a deliverability issue, but it could also signal room for strategy improvement. Be sure to always have a clear call to action to help increase your click rates.

Complaint Rate

A complaint is when a subscriber marks your message as spam. Every time you receive a complaint, your sender reputation is decreased. It’s expected to receive some complaints, but an elevated complaint rate can cause your reputation to drop significantly.

A complaint rate of 0.1% is considered normal. You can think of this as one out of 1,000 subscribers can mark your message as spam and there’s no need for concern. If your complaint rate is > 0.1%, you’ll likely see damage to your sender reputation and will need to audit your list. We talk more about list quality below.

7 action steps to improve your sender reputation

While I'm always excited to take a deep look at customers' existing strategy and list health to identify changes that could improve inbox placement, there are actually a few things you can do on your own to narrow down the cause of a potential downturn in your deliverability. Here's a quick to-do list to assess your deliverability needs:

  1. Be sure you aren’t sending from a free domain such as,,, etc. Doing so will cause messages to either bounce or go to spam. You can read more on this here.
  2. Now that you’re sending from your own domain, be sure it has a valid MX record. You can check your MX record here. If you need help creating an MX record, you’ll want to contact your domain host.
  3. Make sure you aren’t experiencing listbombing. This is the most common reason we see open rates decline. Learn more about the signs of listbombing and how to solve it here.
  4. Are you sending your message to the same domain that you’re sending from? If so, it’s normal for the message to go to spam. Try testing with an email address that doesn’t have the same domain as your sending address. If you need to email subscribers that have the same domain as you, you’ll want to allow ConvertKit within your domain’s settings.
  5. Are you using DMARC authentication on your sending domain? You can check to see if you are here. If so, you’ll need to verify your domain within ConvertKit.
  6. If your email is too large, it might be getting clipped. This means mailbox providers are shortening your email and are not loading the open tracking pixel which could make your open rates uncharacteristically low. Be sure your message size is <100KB. To test this, send the email to yourself, download it, then look at the file size of that download.
  7. Last but not least, be sure to check your “Cold Subscribers” tab often and clean out unengaged subscribers. The more your Cold Subscribers list piles up, the higher the chance you’ll start to see open rates decrease and spam filtering increase.

I hope this helps you have a deeper understanding of deliverability and how you can reach your subscribers' inboxes. If you ever need extra support after implementing these sender reputation best practices, please don't hesitate to reach out to our Support team who will be happy to dive in.

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Alyssa Dulin

Alyssa is a Deliverability Lead located in Nashville, TN. She loves helping senders reach the inbox of their subscribers. Outside of work, Alyssa enjoys traveling, indoor cycling, and spending time with family.

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