• Blog
  • How a sender’s domain reputation affects deliverability
Valentina Pacitti
15 September 2020
Reading time: 5 min.

How a sender’s domain reputation affects deliverability

One out of five marketing emails does not reach the recipient’s inbox (Return Path). A leading cause is the sender’s reputation. Let’s see which factors cause bad reputation and how to prevent email providers from filtering the messages you send to your database.

It’s a fact: between 20 and 25% of the emails you send end up in the spam folder of your contacts. Sometimes it’s because of flawed email design, but more often than not, ISPs block your message because you’re considered an unreliable sender. This means the problem is your domain reputation.

You may think that nothing in your marketing activities could trigger the email provider ban of your contacts. But a behavior that’s not totally transparent, an unprofessional sending platform—meaning, insecure—or the rush to reach as many users as possible may sometimes compromise a good Email Marketing strategy.

Activate now the free trial to discover MailUp's potential.

From developing integrations to strategic support, from creating creative concepts to optimizing results.

What’s reputation of the domain or sender reputation

Sender reputation means the reputation that an IP address has as a sender of email messages. ISPs (Internet Service Providers) take this into account when deciding whether an email should be delivered to the main mail folder (to then be seen and likely read by the recipient) or whether it goes to junk mail.

ISPs are a bit like the assistant who sorts the boss’s mail: it’s the first filter, setting aside all the most relevant communication—personal letters, bank correspondence, bills, fines… —from unsolicited advertising and communications without a sender or from an unknown sender. The first goes to the boss’s desk, the others end up in the trash.

The goal of the email provider’s filtering system is to keep emails that are potentially fraudulent or uninteresting for the recipient at bay. Starting with sender reputation is a logical first step, isn’t it? For sure you do the same when getting mail (both paper and digital): first, you look at who’s writing you.

All previous activities initiated by an IP address are considered in the sender’s reputation analysis. Based on the domain’s history, ISPs decide whether the message reaches the recipient or ends up in spam.

So let’s see how you can improve the deliverability of your mailings by perfecting your reputation.

Factors that contribute to the sender’s reputation

Hundreds of factors affect sender reputation that can either benefit or penalize you when sending your email campaigns. Not all of them are known, but we have a grasp on some:


Using authentication protocols (SPF, DKIM, DMARC) to confirm your legitimacy as a sender to email clients can affect the ISP’s final decision. This is definitely the first step in making sure your messages get to their destination.

The percentage of unknown recipients or invalid email addresses

When you send a message to a recipient who does not exist or is no longer active, the ISPs send you a bounce code to warn you that the destination address is inactive and that you need to remove it from your lists. Ignoring this report sends negative feedback to mail providers.

User reporting for spam or junk mail

If you know you’re not sending inappropriate messages to your contact base, then check that the link to unsubscribe from your mailing list is clearly visible and works. Sometimes, users report a newsletter as spam because they don’t know how to unsubscribe from it.


Many of the users who don’t open your emails or engage with them tell ISPs that the contacts in your database are uninterested in your content, so they won’t see it. For a better experience, providers consider users’ previous interests in their filtering decisions (message opening rates, time spent viewing, clicks, replies, etc.).

Sender recognition

Using a custom domain or entering the company name in the subject are best practices that help the recipient trust you, while sending a positive signal to the provider.

Blacklist presence

Blacklists involve IP addresses that anti-spam organizations and email providers report as known sources of spam. If a sender is on one of these lists, then the filtering system blocks them and sends them to junk. To check if a domain is blacklisted (e.g. the server address for your Email Marketing mailings), use an online service like Mx Tool BoxWhat is my IP address, or Blacklist Alert.

Shared IPs and problems caused by SMTP (Simple Mail Transfer Protocol)

The servers associated with the main providers are based on unmonitored shared IP addresses, meaning a sender who submits valuable content to their database could find themselves sharing an IP with that of a spammer. Obviously, this can compromise your reputation and deliverability.

Sending frequency

Low sending volumes can ring alarm bells for ISPs since it flags a sketchy sender.


Be careful with your reputation as a sender. Here are some best practices:

  1. don’t purchase or rent contact lists;
  2. monitor your mailings—if you notice something strange in terms of deliverability, then check your IP address. You can check your IP’s reputation online with services like:
    1. Talos Intelligence
    2. Trend Micro Ip Reputation
    3. Symantec Ip Reputation
  3. use professional sending platforms;
  4. ask users to whitelist you when subscribing to your mailing list or click the “Not junk” button when they get an email from you. Not everyone will do this. But increasing the number of people who’ve got you in their address book sends a positive signal to the ISPs, and these will be more inclined to deliver your messages to the recipient’s main mail folder.
Share this article

Valentina Pacitti

Copywriter and translator since 2012, in charge of SEMrush Italia's blog since 2015. Words are my means of communicating with people - I read and write plenty of them. I like to know them inside and out, so that I can pick the best ones for every story I'm telling. Simple, clear, precise - this is the writing style I prefer. I'm more offline than online, but you can always find me on my social channels to discuss ideas and projects.

    Subscribe to our newsletter