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How to Optimize Your Email Deliverability and Maximize Your Email Marketing Revenues
11 min read

How to Optimize Your Email Deliverability and Maximize Your Email Marketing Revenues

How to Optimize Your Email Deliverability and Maximize Your Email Marketing Revenues

In this guest post, Julia Gulevich of G-Lock Software, explains how to build and maintain a good sender reputation. She'll walk through the proper sending infrastructure that ensures great deliverability, and explain how to maintain email lists and how to handle recipient actions such as bounces, unsubscribes and engagement. The objective of this post is to ensure that when you're sending mail that people want, they will get it; and if they do not want it, you will know where the problem is and how to fix it.

Sending email is easy. Sending it consistently to the inbox is hard. We will share best email practices you need to follow to have your emails delivered to Inbox whether you are using an email service provider or in-house email sending system like EasyMail7.

We'll look at what you need to do to maintain a good reputation with Internet Service Providers and how to set up your sending infrastructure for maximum inbox deliverability.

To make it easy, I broke it down into 5 chapters:

  • How to Build and Maintain Good Sender Reputation
  • How IP Addresses, Sending Volume, DNS, and Authentication Affect Deliverability
  • How to Maintain Email Lists: Handle Bounces, Unsubscribes and Spam Complaints
  • How Recipient Engagement and Whitelisting Determine Inbox or Spam Placement
  • How to Write Content that Doesn't Trigger Spam Filters

1. How to Build and Maintain Good Sender Reputation

Due to it's availability and ease to transmit information to users, email is being abused by spammers. Thus, to protect their users against unsolicited mail, Internet Service Providers, such as Gmail, AOL, Yahoo and MSN/Hotmail, have declared a war to spammers and have adopted more thorough methods to filter out spam. One of them is sender reputation monitoring.

Reputation is one of the most important assets you have in the email world (just like in real life). If the reputation associated with your domain and IP address is bad, your email will get caught by the ISPs' spam filters and will not reach your recipients' inboxes.

Obviously, a bad reputation will hurt you. But a neutral reputation will also hurt you. If ESPs don't know you, they will assume the worst and filter your emails, at least at the beginning.

The factors that create your sender reputation include:

  • Sender IP address
  • Mailing list validity
  • Complaints
  • Bounces
  • Content relevancy
  • Mailing frequency
  • Mailing infrastructure
  • Authentication

Many enterprise system filters still rely on content, but major Internet Service Providers are moving toward reputation-based systems to determine if the email is spam or not spam.Thus, it's important that you monitor your sending statistics and answer these questions:

Are all your emails being delivered and if not, why? Are messages bouncing due to invalid addresses or spam content? Are users complaining about receiving spam from you? Are users engaging with your emails by opening them and/or clicking links?

You should have all this data to make sure that you are complying with ISPs' guidelines. And if you are not, you should adjust your email sending program to stay in their good graces. Regardless of the Email Service Provider or email software you are using to send emails, you can build up a great email sending reputation if you follow these rules:

  • Only send emails to people who have signed up at your website, application, or service;
  • Always ask the subscriber to confirm their subscription and validity of their email address (so-called "confirmed opt-in");
  • Send only the requested content;
  • Do not send to people who have unsubscribed or complained of spam;
  • Track your email campaigns and exclude inactive users who have not opened your emails within the last 6-12 months depending on your sending frequency.

2. How IP Addresses, Sending Volume, DNS, and Authentication Affect Deliverability

Dedicated vs. Shared IP

Because ISPs consider the IP address when they evaluate the reputation of an email sender, you should keep in mind these two things:

  1. Use a static IP address for email sending so that your domain(s) and IP address(es) build a reputation together.
  2. Your sending IP address and surrounding IP addresses should have a good reputation. ISPs and blacklists sometimes block entire subnets of IP addresses if any of the IPs have a bad reputation.

It is better that you have a dedicated IP address for your mailing campaigns in order to build your good reputation, and not share the reputation with others. If there is one bad apple in the bunch, the reputation of every client sharing that IP suffers.

This explains strict terms of use Email Service Providers have for their clients. In order to provide a good Inbox deliverability to all the clients, ESPs are forced to require confirmed opt-in lists from their clients and watch the sending activity of each user closely. If a user's mailing activity is questionable, the ESP can suspend the user's account.

Besides that, ESPs can rate limit the emails based on the IP. So if you are planning to send a high volume of emails, you should consider getting a pool of IP addresses. Therefore, a lot of email marketers switch to hybrid email marketing systems like EasyMail7 where they can use a dedicated SMTP server with a dedicated IP address.

With a dedicated IP, you have your reputation and deliverability in your hands. If it suffers, it's not because somebody else sharing the IP address with you suddenly became a spammer. It's because you did something wrong and it's on you to check out all the stages of your email marketing program (from list building to email design) to discover and fix potential issues.

Sending Volume

Now you might be wondering: How does the sending volume affect deliverability? Does it matter if you send much or fewer emails?

In fact, what matters is not the volume, but consistency. Your reputation and deliverability can suffer if you are not sending consistently from an IP. If your mailing activity is unstable with sudden rises of volume, ISPs may consider those rises as spam. On the other hand, if your overall volume is too low, ISPs won't assign you reputation. The trick is to balance frequency and volume.

When you get a new IP address, don't start sending right off the bat. "Warm it up" gradually. Start sending at a low rate, then gradually increase that rate. If you send tons of emails right away, the emails will get filtered or blocked by the ISPs. In some cases, ISPs won't even notify you that they are blocking your messages.

To test your email deliverability at different ISPs, use GlockApps. The report will show you whether or not you have deliverability (filtered as spam or blocked), authentication and blacklisting issues, and email spam score.

The next thing to consider, if you are sending high volumes of email, is use separate IP addresses for your marketing and transactional messages. By using separate IPs, you eliminate the problem when your time-sensitive transactional emails may be queued behind a large volume of marketing emails; and you ensure that the delivery of transactional mail is not affected by the reputation created by your marketing activity.

DNS and Authentication

In addition to the IP address, your sender reputation is tied to your domain name (Domain Name System). For the same reasons why it is recommended to use separate IP addresses for marketing and transactional emails, it is a good idea to have separate domains or subdomains for your marketing and transactional mail.

For example, you could use your top domain for your transactional mail and create a different domain or subdomain for your marketing campaigns. Here are some more recommendations when it comes to DNS and authentication:

  • Use the same domain in the email From field as the actual domain sending the message. Hotmail is especially scrupulous about this and likes to filter the messages as junk mail if the two domains do not match.
  • Point MX Records to your sending domain. Some Internet Providers check if MX Records for the domain are valid before accepting the email.
  • Make sure you have proper authentication records at your DNS provider: SPF, DKIM, and ReverseDNS. If your authenticate fails, ISPs will assume you are sending spam and will filter or just drop your email. You can always test your authentication with GlockApps.

3. How to Maintain Email Lists: Handle Bounces, Unsubscribes and Spam Complaints

Email marketing starts with an email list. The primary reason why marketers start having deliverability issues is because they have a bad mailing list. In this chapter, we'll look at such important topics as how to get and maintain email lists, and how to process bounce emails and spam complaints.

You know that it's easier to prevent the disease than remedy it. It's the same in email marketing and deliverability. It's very difficult to solve filtering and blacklisting issues if your reputation is spoiled. Thus, you should remember these list building truisms once and forever:

  • Never purchase a list or scrape web sites for emails. Such lists have a lot of bad email addresses and include spam traps. ISPs have been very good at recognizing bad mailing lists and you will pay the consequences.
  • Only send marketing emails to people who subscribed to receiving your emails on your website.
  • Ask the recipients to confirm their subscription by sending a verification email with a confirmation link (confirmed opt-in). This is to make sure that their email address is valid and that they are the person who signed up.
  • Verify your list for bad addresses if you have a stale list. People can change or abandon email addresses. So, a big portion of your list may turn to be invalid if you have not emailed it for a long time. Thus, use an email verification service such as DataValidation to check your list for validity and delete invalid addresses from it.
  • Have your Privacy Policy on your website or at least on the subscription form.

Bounce, Unsubscribe and Spam Complaints Handling

A big part of maintaining your email list is processing bounces, unsubscribes and complaints properly. In order to receive bounce messages, it is a good idea to set up a separate account for returned emails (for example, [email protected]) and use it as your Return email address for your message. Most mail servers send bounces at the Return email address. However, some send bounces at the from address. So, you should set your bounce handling system to check both accounts for bounce emails.

It's important to separate hard and soft bounces. Hard bounces resulting from invalid email addresses and nonexistent users must be removed from your mailing list forever. Soft bounces resulting from temporary delivery issues can be re-tried several times. After 5 failed attempts, they should be considered as hard bounces and excluded from your campaigns as well.

You must process the bounce data promptly because if you continue sending to bounce addresses, your emails will be filtered and eventually dropped. Processing unsubscribe requests is as important as handling bounces. If you don't do it, the recipients who do not want to receive emails from you anymore are more likely to click on the spam complaint button, which will cause more harm to your reputation. Plus, many ISPs look for the unsubscribe link in the email and if they don't find it, they are more likely to filter the email.

With EasyMail7, you can organize handling of unsubscribe emails either online or via email. The program automatically stops sending messages to the recipients who have unsubscribed.Furthermore: Most of the major ISPs provide feedback loops through which they notify the senders about spam complaints. You can find links to feedback loop signup pages here. It is recommended that you sign up for these feedback loops, monitor the feedback you are getting and take steps to exclude complaining users from your list. If you ignore the complaints, ISPs will throttle your emails and eventually block them.

In addition to bounce and unsubscribe handling, EasyMail7 can process spam complaints automatically and stop sending to the recipient after a complaint. Email marketers can also know the quality of their email list prior to sending mail to it. Get a Free Email List Quality Report from DataValidation and know where your list stands prior to putting your reputation on the line.

4. How Recipient Engagement and Whitelisting Determine Inbox or Spam Placement

Besides bounces, complaints and unsubscribes, ISPs measure your reputation and decide where to deliver your emails to based on the engagement of your subscribers. If your subscribers are opening, forwarding and replying to your emails, it improves your reputation with a particular ISP and your emails get more chances to be delivered to the Inbox. It is also helpful if people add your email address to their address books or safe sender list.

With that said, it's important that you send engaging emails. Not only is it good for your business, but it also helps you overcome ISPs spam filters. With G-Lock Analytics, you can track opens and link clicks for your email campaigns and estimate how engaging your emails are. Now, what about whitelists? Being added to a whitelist (the opposite of blacklist) is like getting a green light at an ISP.

While not all ISPs have whitelists and not all rely on them, it is still a good idea to get added to whitelists where they are available. To do this, you will most likely have to provide some history of your sending activity. Plus, most of the ISPs require that your have a dedicated IP address for email marketing.

Return Path has a certification program that whitelists you at the major ISPs such as AOL, Yahoo, Microsoft, Comcast, Cox, Cloudmark, Yandex,, Orange, and many others, including key international domains. Also, certified members benefit from unblocked by default images and active links and from bypassing critical mailbox-provider filters.

5. How to Write Content that Doesn't Trigger Spam Filters

When you write an email message to your subscribers, the first rule you should follow is "send relevant and engaging content." But besides relevancy, there are a few more things to consider to minimize the spam score of your email and risk being filtered to the Junk folder. Here is a quick checklist of the elements in the message content that can trigger spam filters:

  • Misspelled and spammy words, ALL CAPS and excessive exclamation marks!!!!!!!!!!!!!, too much color and bold text
  • Deceptive and misleading Subject lines
  • Too many links and images, big image ratio vs. text ratio
  • Broken HTML (invalid HTML tags in the message source can work as spam filter triggers)
  • Absence of the unsubscribe link (many ISPs, particularly Hotmail, pay attention to it and if the link is not there, you are likely to get filtered)
  • Shortened URLs that are frequently used by spammers
  • URLs from untrusted domains
  • Images hosted on crappy sites
  • Different domains in the "From" field, return-path, and message-id

You should always test your emails before you hit the "Send" button!

What's the bottom line?

Email marketing is about deliverability. No matter how relevant and engaging your message is, you've spent time in vain if your recipients don't see your email. Deliverability is a complex topic that includes tactics on sender reputation, authentication, infrastructure, list building and maintenance, recipient engagement, content writing and testing. Marketers should consider all these topics when they decide to start sending email campaigns.

To avoid deliverability issues, you need to understand what you need to do to have your emails delivered to the Inbox and follow best email marketing practices. If deliverability is already an issue, you have to understand what you did wrong and how to fix the problem. To uncover an email deliverability problem, you have two powerful tools in your hands: tracking and testing.

Email tracking allows you to monitor your response rate from email to email. If there is a sudden decline, that might be an indicator of an Inbox placement problem. It's also a good idea to check the tracking report per domain and see if you have no opens or clicks from the recipients on a particular domain. If that is the case, you are most likely being blocked by that ISP. You can use Litmus Email Analytics to measure opened emails' performance.

Testing is another powerful thing that can serve you. When the deliverability issues happen, start with testing the content of the email, including subject lines and URLs within the content. You'll determine whether or not any of those elements is causing the email to be filtered or blocked. In addition to content, test your authentication records and your sending IP address for blacklisting issues. Blacklists can be a serious barrier on the email's way to the Inbox.

When the issue is identified, take steps to fix it. If it is email content or subject, re-write it, remove or change URLs. If the issue is tied to authentication, ask your email service provider or SMTP server admin for help. If your IP is blacklisted, visit the blacklist website and go through the removal process.

If after doing all things above, you continue having deliverability problems, you should think about changing the sending IP and domain and start building a reputation for your new IP and domain considering best email marketing practices outlined in this Email Deliverability Guide.

Did you find this Guide useful? Check out other articles on email marketing, deliverability best practes, and tips and tricks on G-Lock Software's Blog.