8 Factors That Influence IP Reputation and Email Deliverability

May 25th, 2021

Getting your email marketing messages into your recipient’s inboxes is key to a successful mailing campaign. This is “deliverability.” One of the central factors governing the deliverability of your messages is the reputation of the Internet Protocol (IP) Address of your sending email server — its “IP reputation.”

This article explains some of the most common factors that affect your server’s IP reputation and email deliverability. Having a good IP reputation will help ensure your marketing messages are reaching your recipients.

Before diving in, check to see if you are on any common blacklists using mx toolbox.

ip reputation and email deliverability

1. How many messages has your server sent?

If your server has not sent many emails, then it is a relative “unknown” on the Internet. It has little or no existing reputation. This is okay as long as you do not suddenly start blasting out huge amounts of email. That would be seen as a “red flag” to filtering services and cause your server’s reputation to go down or blacklisted. When your server is blacklisted, it is labeled as an unreliable or untrustworthy sender. Emails sent from a blacklisted server are often flagged as spam and will not reach your recipients’ inboxes.

When starting to send emails with a new server, your best bet is to “warm up” your server’s IP address. This involves sending small mailing blasts of a few thousand messages at a time and slowly increasing the size of your mailings over the course of a few weeks. This serves to introduce your IP to the world in a smooth and cautious way that spam filtering services appreciate.

2. How many of your messages have been marked as Spam by your recipients?

Recipients who don’t really want your email will often mark it spam rather than unsubscribing or deleting the messages. This, unfortunately, makes it look like you have sent them spam, even if they subscribed to your mailings! The more this happens, the worse your IP reputation can become.

You should subscribe to feedback loops (or use a mailing service that includes them) so you can be notified when folks do this. You can unsubscribe anyone who complains of your email in this way, preventing them from complaining in the future and thus minimizing the number of complaints (legitimate or not) against you.

3.  How often is your server trying to deliver email messages to invalid email addresses?

Even well-maintained mailing lists may contain some email addresses that are invalid, as people change addresses frequently. However, purchased email lists, old lists, and lists acquired via illegitimate methods, will often contain large numbers of invalid addresses.

If your server tries to deliver messages to significant numbers of invalid addresses, that will be noticed and your reputation will go way down — your server will look like it is run by a spammer.

Use new opt-in lists to avoid spam flags. Make sure that you remove addresses that are bouncing right away — so that you do not keep trying them over and over on every mailing.

4. What is the rate that you are trying to deliver your messages?

Faster is not always better. The more messages you try to deliver in a short time, the more likely your recipient servers are going to put up walls to throttle your sending or block you altogether. Many recipient domains, most notably Yahoo!, have explicit low limits on the number of messages they will receive from an IP address in a given period of time. If you try to push beyond that, you shoot yourself in the foot. It is best to (a) deliver the messages more slowly and (b) use multiple servers and thus multiple IP addresses in tandem if you need to increase your mailing throughput without tripping on recipient rate limits.

5. Has your server’s IP address been blacklisted anywhere for sending spam or other types of unwanted email?

A blacklisted server has a decreased IP reputation. You should remove your IP address from any blacklists and seek to ensure that your mailing patterns do not land you on any new blacklists.

6. Is your IP address static and set up properly by your ISP?

If you are mailing from a server at an ISP (e.g. Verizon, Comcast, cox, etc.) or from a virtual machine in the public cloud (e.g. Amazon, Rackspace, etc.), then your IP reputation is automatically lowered because that IP can be used by many different people over time and can often change hands without notice. Use an IP address is not changeable (dynamic), not owned by your ISP, and not in a public cloud.

Also, make sure that there is a valid “Reverse DNS” entry for your IP address and that it matches the hostname of your server. For example, if your server’s name is “joes-mailer.com” then “joes-mailer.com” has a specific IP address (e.g. If you look up what name goes with “” it should say “joes-mailer.com” and when your mail server talks to other servers it should say “Hello, I’m joes-mailer.com.” If these things do not all match up, then your server’s IP will look sketchy.

7. Are other people using your server for sending email? What are they doing to your IP Reputation?

If you are sending email through a server shared with other people, or the mail is going out through IP addresses that are not dedicated to you, then you are not in control of your own reputation. These other folks could suddenly start sending spam, degrading the reputation of the IP that you use, and harming the deliverability of your messages.

The best solution is to use a dedicated mailing server that no one else can access. In this way, you can control exactly what gets sent through it. You are in control and there should be no surprises.

8. Have others used your server or IP before you? What is their legacy?

Let’s say you set up a new server and a new IP address. This IP address was used by other folks before it was assigned to you. If these folks were not good custodians, your could have been assigned an IP address with an existing poor reputation! If that happens to you, your best bet is to either get a new address or to:

  • de-list the IP from any blacklists
  • wait a few weeks before you use the IP for your own mailings
  • warm up the IP by sending small mailings of solid non-spam-like messages to known good mailing lists

This should bring the reputation back up to good standards.

When it comes down to it, your IP reputation is based on your mail server provider, your configuration, and your behavior.  You can pick a good provider, proactively control your behavior, send good messages to good opt-in mailing lists and have excellent deliverability.

Talk to one of experts to learn more about how an excellent IP reputation affects your delivery success.