Everything Email Marketers Need to Know About Sender Reputation

8 Important Factors That Determine Your Sender Reputation

When it comes to email marketing, deliverability means getting email marketing messages to the recipients' Inboxes. It is the key to a successful email campaign.

Over the past years, email deliverability has evolved. While the subject lines, spam filter triggering words, special characters, and image-text ratio have been the most important things to pay attention to in the past, these days, email deliverability depends mainly on the sender reputation which includes the sending IP reputation and sending email/domain reputation, recipient’s engagement, list acquisition, and list management practices.

In this post, I reveal eight factors that impact your sender reputation. You can go through the list to make sure that all the factors are in good order to maintain your good reputation and increase the number of Inbox placements for your marketing email messages.

Now, here the factors that determine your sender reputation (and consequently impact your email deliverability):

8 Important Factors That Determine Your Sender Reputation

1. How often your server sends email messages to invalid email addresses.

It is about your list acquisition and maintenance practices. Purchased email lists, harvested lists, old lists, and other lists created using not opt-in methods often contain a lot of invalid addresses. And even well-managed email lists may contain some invalid email addresses as people change addresses frequently.

If your mail server often attempts to deliver messages to many invalid addresses, it will look like a spammer's activity and your reputation as a sender will go down.

With that said, collect email addresses using a confirmed opt-in method and verify old opt-in lists for validity to make sure that you remove addresses that will bounce right away. After each mailing, add hard bounce addresses to your "do not send" list so that you do not keep sending to them over and over again.

2. How many recipients mark your emails as spam.

It's sad, but spam complaints happen even if people subscribed to your mailings. They may find your content irrelevant, or they may forget that they subscribed to your list, or they may not see the unsubscribe link, etc., etc. — hence, they hit the "This is spam" button and file a complaint against you.

Unfortunately, the more complaints happen, the worse your sender reputation becomes.

To reduce complaints in the future, you should subscribe to feedback loops service (or use an email service provider that includes it) with ISPs so they notify you when a user sends a complaint. You can find links to feedback loop pages with most popular ISPs here.

You must unsubscribe or remove everyone who complains of your email, preventing them from receiving your messages in the future and thus minimizing the number of complaints against you.

Read:  Gmail Puts Emails to Spam. How Can I Fix It?

3. How many email messages you sent from that IP address.

If your IP address is rather new or if you have not sent a lot of emails from it yet, the IP has little or no existing reputation. It is OK if you do not start blasting big email campaigns one day.

But if you do, your mail server would look like a machine compromised by a spammer and raise a "red flag" to filtering systems and ISPs. The consequences can include the downgrade of your server's reputation and blacklisting.

To protect your new IP address, take the time to "warm it up." Start by sending small blasts of a few thousand messages at a time and slowly increase the volume over a few weeks. This way, you'll introduce your new sending IP address to the Internet world in a smooth and safe way that spam filtering services will appreciate.

A good scenario of the IP warm up is:

Day 1 – 1000 relays per day and 100 per hour

Day 2 – 2500 relays per day and 200 per hour

Day 3 – 3500 relays per day and 300 per hour

Day 4 – 4500 relays per day and no hourly limit

Day 5 – 7500 relays per day and no hourly limit

Day 6 – 9000 relays per day and no hourly limit

Day 7+ – no limits

If you are using G-Lock EasyMail7, you can set the limitations per hour and per day in the Outgoing Mail Account settings to be sure you are not exceeding the volume of sent messages each day.

4. How fast you try to send the messages.

Some ISPs, most notably Yahoo!Mail, limit the number of messages they can receive from an IP address within a given period. When you push beyond that limit, you put yourself into a "red zone".

So, sending faster is not always better. Often, it is better to send the messages slowly or use multiple servers and thus multiple IP addresses if you need to deliver a time-sensitive email urgently without violating the recipient rate limits.

5. Whether or not your server's IP address is blacklisted anywhere.

Blacklists can dramatically alter your ability to deliver email. If your sending IP address is blacklisted, that significantly decreases your IP reputation. And a bad IP reputation is one of the common reasons ISPs block email messages.

You'll want to check whether or not your IP address you're sending messages from is on any of the common blacklists using the GlockApps email spam checker.

IP reputation monitoring from GlockApps
IP reputation monitor report

It's important that you work to get your IP address de-listed from any blacklists it ever gets on and watch that your mailing activity does not lead to blacklisting issues again.

Read:  How to Remove Your IP Address from the Yahoo!'s Blacklist

Besides public blacklists, your IP can be blocked by particular ISPs. Gmail, Hotmail, Yahoo and other providers maintain blacklists of IPs seen to send spam to their users.

Below are good guides you’ll want to check to learn how to find out if your sending IP is blacklisted by an ISP and how to request the removal:

How to Remove Your IP Address from Gmail’s Blacklist
How to Remove Your IP Address from the Hotmail/Outlook’s Blacklist
How to Remove Your IP Address from the Yahoo!’s Blacklist

6. Whether or not your server's IP address dedicated and static.

When you are sending from a shared IP address, you share the sender reputation with other users, and someone else's mailing activity affects your ability to deliver messages. If one user is sending emails that are absolute garbage, his tactics are not only unhelpful but really harmful to others. One sheep spoils the whole herd.

With a dedicated IP address, only you are responsible for building and maintaining the reputation of your sending IP address. You control what exactly is sent through it, and there should be no surprises.

Even within a brand, you'll want to have a dedicated IP address for your transactional emails which is separated from marketing emails because transactional emails inherently have a really good reputation, and you really want to make sure people get them. It's super important, and you don't want a bad campaign to impact your transactional emails.

Also, be sure that your sending IP address does not change (static) and not in a public cloud.

7. Whether or not your server's IP address have authentication records.

Authentication helps protect from email forging and prove that you are the sender who you say you are. Email messages that do not pass authentication checks may be blocked or are subject to additional filters, potentially preventing them from coming to the Inbox.

Plus, authentication is essential for protecting your brand and preventing forged messages from damaging your sender reputation. Many Internet providers use authentication, among other things, to track sender reputation.

There are different methods to authenticate the sender such as SPF, DKIM, rDNS. There is no agreed best method for authentication, and different ISPs can use different methods to check the sender’s authenticity. That's why it's important to have all authentication records set up correctly.

Thus, if you use your own SMTP server with an in-house email system, implement outbound email authentication with valid PTR, DKIM, and rDNS records.

Here you can read the complete guide about email authentication.

You can use the GlockApps service to test your authentication records and make sure they are in the “green” zone.

Read:  Diagnosing Delivery Issues with Your Own Data

Authentication test from GlockApps
Authentication test from GlockApps

And last, but not least…

8. Whether or not others used your server or IP before you.

Imagine that you've just set up or got a new server and a new IP address. The bad thing is that this IP address might have been used by other marketers before it was assigned to you. And if those folks were not good senders, your new IP address may already have an existing poor reputation. If that happens to you, your emails are doomed to land in the spam folder or be blocked.

Thus, before you start actively sending from your new IP, it's recommended that you do this:

– check your new IP against blacklists and de-list it if it's listed anywhere;
– wait for a few weeks before you start sending your own mailings from that IP;
– "warm up" the IP by sending small volumes of good non-spam messages to quality opt-in mailing lists.

This practice should restore the bad reputation to good standards.

When it comes to your sender reputation, it is based on your mail server provider, your configuration, and your recipient's behavior.

You can choose a good provider, set up authentication records, build a quality confirmed opt-in list to minimize spam complaints and bounces, and send good messages with relevant content to enjoy excellent deliverability.

For more information, you’ll want to check this complete guide about the best email deliverability practices that really work.

Test Your Deliverability and Spam Score

Everything Email Marketers Need to Know About Sender Reputation

Testing email deliverability using a testing tool such as GlockApps will help you identify potential filtering issues before you send.

Within minutes, GlockApps will show you where your email is placed at different ISPs.

To generate the report, we’ll re-send your email through our personal accounts with Amazon SES, SendGrid, and Mailgun to the control list of email addresses (seed list).

But you should be aware that the deliverability may be different when you send emails through your SMTP server, delivery service or email service provider.

To test deliverability through YOUR sending infrastructure, you’ll need to create an account on GlockApps.

In your personal account, you’ll be able to create new tests and we’ll show you in real-time if there are any problems with YOUR sending system and message.

So, quick-test your email using the live test below and you’ll find the “Create My Account” button in your quick report.

We’ll show you where your email appears: Inbox or Spam

Send a copy of your email to:




Julia Gulevich is an email marketing expert and customer support professional at GlockSoft LLC with more than 15 years of experience. Author of numerous blog posts, publications, and articles about email marketing and deliverability.