BlogDeliverabilityI’m not a spammer, how did I end up on a blacklist?!

I’m not a spammer, how did I end up on a blacklist?!

3 min read
SMTP relay service

You’ve checked the boxes on email engagement 101: a compelling subject line, high-value content, an offer your recipients can’t refuse. Then you find out your sending IP is on a few blacklists and your emails can’t reach recipients. I’m sure your first thought is “I love it when ISPs block my messages!” (said no one ever).

You immediately begin to pick apart your emails to figure out why you got blacklisted in the first place. It’s certainly not the end of the world, but it does throw a wrench in your email marketing efforts.

4 ways to get yourself on a blacklist

To zoom in on what’s putting you on the fast-track to poor delivery, let’s look at blacklists and other reasons mailbox providers aren’t accepting your messages.

Reputable Blacklists

Maybe you’ve used keywords like “free” one too many times to promote offers, or perhaps your “from” address is a distro list and doesn’t seem very personal. It doesn’t always come down to the way your emails look or sound to reputable blacklists. So, what makes these ‘reputable’ anyway? Reputable blacklists originate from trustworthy entities that police the internet for bad actors. They can detect if the IP addresses from the computer or server you’re using to send email are responsible for spreading spam. When used by ISPs to decide if your messages will pass through, they can stop over 80% of connections.

Reputable blacklists have specific triggers that they look for to decide if you’re going to be placed there. These include things like known spamtraps, spammer email addresses, or a sudden increase in contacts that are added to your sending list. If you haven’t maintained your list to keep out these kinds of addresses, or slipped to the dark side in desperation and purchased a list of contacts that did not give their consent, hold on tight, you’re in for a bumpy ride!

Follow us
via email
Follow us via email
Stay on top of everything that matters in email marketing

Stay on top of everything that matters in email marketing

By signing up for our newsletter, you’re agreeing to the terms and privacy policy
located at the
bottom of this page.

High Complaint Rate

A common misconception about blacklists is that they single-handedly block your emails from reaching recipient inboxes. Even if you’re on a blacklist, it doesn’t necessarily mean that this will impact the delivery of your message. Mailbox providers take into account your feedback loop (when available) as part of their decision-making criteria to determine if your message is going to make it into the recipient’s inbox. Part of this feedback loop includes a metric they weigh heavily called complaint rate, which can tell mailbox providers whether or not you – as a sender – are following best practices.

Every time a recipient in your campaign marks your messages as “Junk,” it signals to mailbox providers that they are not engaged with your content, causing your complaint rate to increase. Let’s assume you’ve sent your irresistible email offer to 1,000 contacts, and 15 of them have marked your message as ‘junk’:

(15 messages flagged as ‘junk’/ 1,000 contacts targeted) x 100 = 1.5% complaint rate.

Ideally, you want to keep your complaint rate below 0.1% (one-tenth of one percent). Anything higher than this could be the red flag that relegates your message to the spam folder and identifies that there’s something wrong with your sending reputation.

Poor IP Reputation

So, does that mean I don’t have to care about appearing on blacklists because ISPs value complaint rate? Not exactly… you should definitely pay close attention to whether your IPs appear on reputable blacklists.

It could be that your IPs are just new at this point and need some time to warm up, or you’ve been using a shared IP to send millions of marketing and transactional emails. Your unique sending patterns can be traced through IPs, and mailbox providers get to know you by the volume and the frequency in which you send emails. With an established IP reputation – good or bad – you’ve basically set expectations about your email practices, and it can be both costly and difficult to change if your reputation is not where you want it to be. 

IP reputation is just one aspect of sending reputation. There’s also the role your domain(s) play in telling ISPs and mailbox providers about your intentions.

Poor Domain Reputation

Taking a step back, I’m sure you must have asked yourself this question before obtaining your domain(s) for email:

What’s the purpose of the emails I plan to send?

Not looking to trigger an existential crisis or anything, but answering this question is key in deciding what your domain or subdomain name(s) is going to be, what kind of emails you will be sending from each, and if they will be sent from the same IP. All of which have an impact on your domain reputation over time.

Domain reputation is more granular in the sense that it factors in how long you have had your domain(s), and the industry in which you do business. So even if your IPs change over time and with different email delivery partners, there is still a record of your email habits attached to your domain. And, if you have a good domain reputation, the benefit of retaining your domain is evident in other aspects of your business as you’re building a brand that’s also attached to your domain. Since domains are so permanent, some mailbox providers value domain reputation over IP reputation to decide if they trust your intentions.


Ending up on a blacklist isn’t the end of the world, but it can be time consuming and costly to get back on track and in the good graces of both ISPs and mailbox providers. Following best practices to send marketing and transactional email is the best way to protect your sending reputation, and it can be helpful to partner with a deliverability expert to proactively monitor your IP and domain reputation before you become at risk. 

About Mailgun

A Y-Combinator success story, Mailgun is an email delivery engine created by developers for developers. Since 2010, Mailgun has provided deliverability expertise and leading technology via cloud-based email APIs for customers such as Slack, Github, and Shopify. Through its own proprietary technology, Mailgun strives to continuously ensure you can send, receive, and track email effortlessly.

SMTP relay service
Mailgun is email automation created for developers. It uses REST APIs to effortlessly send, receive and track emails.

Get the complete deliverability handbook!

Workflows, and deliverability
knowledge, all in one place.

Get the complete

Workflows, and deliverability
knowledge, all in one place.

Latest posts

Find article by category

Follow us
via email
Follow us via email

Stay on top of everything that
matters in email marketing

Stay on top of everything that matters in email marketing

Your information will be handled in accordance with the Ongage Privacy Policy.

The complete

Read the most significant, most organized volume of information written about email deliverability.

Got cookies?

This site uses cookies for functional, operational, analytical and advertising purposes. Please refer to the
Cookie Policy.