Email Deliverability Guide

In this guide we will explore the process of how your email campaigns go from our WYSIWYG editor in Interspire Email Marketer until finally reaching your subscribers’ inboxes. The important thing to remember about deliverability is that it involves the use of many other components besides just our software, and approximately 90% of the sending problems you’ll experience will be caused by something outside of Interspire Email Marketer.

By the end of this guide you should be more familiar with common trouble spots along the entire email sending process, and how you can best combat these issues to ensure maximum deliverability.

The Process

After creating a campaign in Interspire Email Marketer and getting ready to send it, there are a number of things that happen behind the scenes while your email goes through the course of delivery, finally reaching your subscribers. Firstly, Interspire Email Marketer will add the necessary “headers” to your email which indicate many things, such as the list ID and contact ID, so that if the email is bounced back, we can properly process the bounced emails. There are other important headers that will be discussed later in this guide, such as DKIM signatures, which will heavily increase deliverability.

This message is then relayed to a Mail Transfer Agent, or MTA, which sends the email out towards its destination. In most Interspire Email Marketer setups, this MTA will be on the same machine as the software, particularly if using a shared server hosting package. Each MTA that your message passes through should add a “Received:” header, allowing one to see the path taken en route to your users.

Upon finally reaching the destination mail server, your email will typically be run through a series of tests, trying to categorize the mail as legitimate or spam. Many spam messages typically have forged headers, and more advanced mail servers will attempt to verify that the email originated from the domain indicated in the “From:” address. There are a number of steps that can be taken to better pass these tests and get higher deliverability rates, which will be discussed later in this guide.

Lastly, the final MTA server will send the mail to the recipient’s mailbox. Depending on the email service and the mail client used to view email messages, it may be scanned once more for spam on the user’s machine, before finally reaching their inbox and being opened and read.

The important thing to realize is that across the many different systems and programs that your message will pass, issues can arise. Bounce notifications are a very useful tool to help understand these problems and rectify the issues caused by them, but depending on the system and the exact error, not all problems will bounce back with a helpful notification message. This can be very frustrating and while 100% deliverability will never occur, there are a number of tools we can use to increase deliverability rates significantly.

What Can I Do Within Interspire Email Marketer?

Valid “From:” Email Address

There are a few tools within Interspire Email Marketer itself that will lead to better deliverability. First and foremost, use a “From:” address that is valid, not used for spamming, and most importantly, is owned by you! This may seem like a little step, but please keep in mind that whether you know it or not, you will build an e-mail “reputation” that many servers use to decide whether to let your message pass.

If you attempt to send email and make it appear that it comes from an address other than your own, you stand a high chance of 1) being discovered, as there are tools in place to check that you are who you say you are, and your mail won’t be delivered, and 2) being blacklisted, either locally or on a larger global blacklist. These blacklists can be quite difficult to be removed from and it’s much easier to play by the rules to begin with, which means don’t forge your email address!

Spam Keyword Check

When creating a campaign, there is a rudimentary tool provided to scan your email campaign for common spam keywords. While this is not the only factor used in categorizing spam, and while there are situations where these keywords can be used legitimately, you still need to take care to pay attention for common spam words, as it could play a role in decreased deliverability. You can find it immediately below the text email editor on your Create/Edit an Email Campaign page.Check for Spam Keywords

After clicking the button, Interspire Email Marketer will scan your message, and indicate any problem words or phrases, and also indicate a relative score for each. After totaling all words, it will make a recommendation on how “spammy” your email message will appear to recipients, allowing you to make the final decision to either allow the words or change the wording to something else

Double Opt-in + CAPTCHA

One thing commonly taken for granted is that every user receiving mail is a valid subscriber who wants your email campaigns. Unfortunately, because of the prevalence of bots taking advantage of signup forms, and fickle consumers, this is not always the case. To better ensure the integrity of your contact lists, it’s industry best practice to use double opt-in confirmation and CAPTCHA on all signup forms. This will eliminate almost all bot signups, and will require conscious action by people to bring themselves onto your mailing lists.

The reason the second case can be very important is spam reporting; even if a user legitimately signed themselves onto your list, it takes a very small percentage of users reporting an email as spam before aggressive filters like Gmail and others categorize your campaign as spam system wide. This means that the actions of a few of your users could affect the deliverability of many more users, so it’s best to make people confirm twice before subscribing them to your contact list.

What Else Can I Do?

As I’ve discussed, even though there are basic steps you can take within Interspire Email Marketer, our software is but one cog in the machine, and there are many other common fault points for problems. I’m going to talk in greater depth about some of these problems, and how you can work to get better deliverability. Please keep in mind that depending on your hosting situation, some of these factors can be pretty complex to configure and may require the assistance of a network administrator or webhost to properly implement changes.

Attachments & Total Email Size

If you’re sending very large campaigns, you might notice very low delivery rates. This is because many mail transfer agents cap the maximum attachment size at 10MB. In some cases, the maximum email message (including all attachments) is limited to 10MB also. Keep this in mind, as it can cause problems. Also, you might notice you are close to the limit but not over, and still have delivery problems. In this case, it’s because any binary attachments will be transferred in base64 encoding. This will inflate the size of your data approximately 30%, so keep in mind that just because your attachment was under the size limit when you attached it doesn’t mean it’s under the size limit in the conditions with which it reaches your recipients.


Some emails may bounce because the customer sends too many emails to one domain. Obviously, this is a bit harder to work around, and you may find it necessary to split your contact list into multiple smaller lists if you notice this in your bounce messages often. Also, in rare occasions if a mail server is receiving too many incoming emails it may start bouncing messages instead of delivering them. This is a rare occurrence and the only way to combat this is by sending during low traffic periods for the receiving server.

Real-time Block Lists (RBLs)

Occasionally, you might find that one or more of your email campaigns has resulted in a total lack of delivery to certain domains. This can be difficult to diagnose, because many domains won’t inform you that your system is being blocked, opting instead to drop any mail sent their way. If you notice something like this occurring, it’s probably wise to check RBLs to see if your domain/IP address is listed.

Many mail servers use one or multiple of these real-time block lists, checking the IP address of mail it receives. If your IP address is on the list, chances are any email you’ve sent will be deleted/bounced, and you won’t be able to send to users of that domain until you get your IP removed from the blacklist. This can vary in difficulty to accomplish, and each blacklist has its own policies, so you’ll need to consult them directly for more information on being removed.

DKIM Signing

So you aren’t blacklisted, but your email still doesn’t seem to make it to certain places? The next thing you’ll want to configure is DKIM signing. DKIM, or DomainKeys Identified Mail, is a process by which your mail server places a digital signature into the headers of all outgoing messages. This signature can be checked against the actual domain name, and can be used to determine if the message came directly from the domain itself (rather than another source), and that it has not been tampered with in transit.

DKIM signing is becoming more standard throughout the email marketing industry, particularly as more and more forged emails become prevalent. Some mail servers use DKIM signing to verify email messages, and as such, it’s good practice to have it setup on your outgoing SMTP server to ensure increased deliverability rates.

You can find out more about DKIM at, and you’ll probably need to consult with your webhost or systems administrator to properly configure it, as it will vary depending on your hosting environment, operating system, and outgoing SMTP server/MTA.

SPF Records

Somewhat similar to DKIM signing are SPF records. While they work differently, the concept is still much the same: a receiving mail server should be able to verify that the message they have received came from the person that it says it came from. Receiving mail servers can check the sender’s domain’s SPF record, which is basically an authorization list of who can send mail on behalf of that domain. If the IP address of the sender doesn’t match the domain itself, or isn’t explicitly authorized to send mail for that domain, in many cases it will be bounced/deleted.

You can find out more about the SPF specification at, and also get help on creating an SPF record for your own domain. SPF records are also powerful tools because not only do they let receiving mail servers positively identify your mail, but also let servers categorize people who might attempt to forge your email address correctly, deleting those messages before they can ever reach recipients.


By reading this guide, I hope you’ve become more familiar with the process that brings an email campaign from your the WYSIWYG editor through the internet until it reaches your intended recipient’s inbox. Even though there are steps you can take within Interspire Email Marketer to improve deliverability, a large burden remains beyond the scope of the software. These things include tools like SPF records, DKIM signing, spam blacklists, and MTA configurations.

Deliverability FAQ

What is a split test? How do I use split tests with my emails?

Split tests can be used to compare different versions of the same email campaign based on open statistics or links clicked statistics. So, if one version has been opened more then any other; it will be declared the winner. Your winning email can then be sent out automatically or at a scheduled time of your choosing. Following is a simple step-by-step guide for judging and delivering the most popular version of your email campaigns.

  1. From your Interspire Email Marketer account, navigate to Email Campaigns > View Split Tests > Create a Split Test
  2. Enter a name for your split test
  3. Select which email campaigns will be compared against each other
  4. Choose which method of testing to use
    • Note: Move your mouse over the help icon for more information
    • If you use the “Find a winning email and show me the results” method, the winning email campaign can be scheduled by you whenever you want. Alternatively, after testing a percentage of the list, you can have the winning email sent out after a delay.
  5. Click Save & Exit or Save & Send

Whenever you decide to send the test you will be able to choose which contact list it will be delivered to.

My emails are being marked as spam. What is Interspire Email Marketer doing to cause this?

Any spam filtering that’s going on is always a problem with your server or content, not Interspire Email Marketer itself, so there’s nothing from a Interspire Email Marketer perspective that we can suggest.

Google doesn’t have a very restrictive spam filter so you can try sending emails to a Gmail account. If your emails are being picked up as spam by Gmail it would suggest a server issue on your end. Here are a few things you could try:

  1. Change the content of the confirmation emails
  2. Try a different web hosting provider (your IP range could be in trouble)
  3. Make SURE reverse DNS is on your server. Without reverse DNS, most spam filters will trigger.

I don’t seem to be receiving any emails from Interspire Email Marketer. How do I fix this?

If you’re testing Interspire Email Marketer and don’t seem to be receiving any emails, most likely there is a problem with your server.

Firstly, login to the Interspire Email Marketer control panel and go to the ‘settings’ option. From there, there is an option you can use to test the Interspire Email Marketer emailing system. If you still don’t receive emails when using that test, try sending to a different email account as your spam filter may be trapping the email.

Finally, if all else fails, upload the attached script to your server and run it from the browser. It will attempt to send a basic email to the address you specify. If that doesn’t work, then you will need to contact your web hosting provider to fix the problem.

I send an email campaign, but some contacts don’t receive it even though they receive a preview. What’s going on?

There could be a number of reasons for this.

  1. The contacts are subscribed as Text but you are sending a HTML email campaign. Check that the email type you are sending matches the contacts preference.
  2. A spam filter is picking up the email and blocking it from getting to their inbox. Although the preview may have come through, your email campaign may have had link tracking or open tracking on, which some picky spam filters will use to detect a possible spam email and block it. If unsure, test your next campaign by turning off link and / or open tracking.
  3. The email being sent is being bounced back for a particular reason. Check your bounce account for any bounce emails and see if any match the particular email address that is not getting delivered to. Check to see if there is any specific message or suggestion on how to fix deliverability.

You can also ask a systems administrator for the receiving domain name if they have received the email or if they can search their mail logs to see why the email wasn’t delivered.

I have a lot of mail being delayed at Yahoo. What is happening?

That is normal when you send to yahoo accounts.

They do something called “Grey-Listing” which means they always reject the first attempt to send an email.

The second attempt will work (which your mail server automatically handles for you, you don’t need to do anything to make it go through).

See for more information about how it works.

My emails never get to my test email address. What is happening?

Often the problem with deliverability can be due to you sending emails to your own server.

One way to test to see if your emails are actually being sent and received is to create some test email accounts on other servers and see if you can send an email to these accounts.

Sign up for a Gmail, a Mail account and a HushMail account. Once you have done this send your email campaign to them and check to see if your emails make it. If they do then there will be something not set up right with your mail server.

I don’t receive email campaigns that I send to myself. What’s going on?

The most common reason you don’t receive an email that you’ve sent to yourself is because of spam filters on your email account.

If you are using Yahoo mail or Hotmail, this is a common occurrence due to their very aggressive spam filters. Check your spam or Junk mail folder to make sure the email hasn’t been automatically delivered there.

Some mail accounts such as Yahoo mail can sometimes block an email but it won’t appear in your Junk mail folder or inbox. To work out what is happening, sign up for a free Gmail Account and send your email there. Gmail is a lot less aggressive with spam filtering and will usually deliver all emails. Gmail also has a spam folder so if you don’t see your email in the inbox, check that folder. Finally, if your mail is being flagged as spam, there are usually reasons for this, which can include your choice of words such as “Free” etc.

There may be an issue with mail sending on your server. Contact your web hosting provider to make sure mail can be sent from your server. Finally, if that doesn’t help, please post a support ticket and we’ll try and find out what the problem could be.

My Email Campaigns and Autoresponders seem to get sent to the Hotmail junk folder. What can I do?

Hotmail and other large email providers are placing very heavy restrictions and regulations on their incoming emails in an attempt to help stem the flow of spam emails.

There are a few things that you can do to help in getting your emails into the intended inbox:

First you can setup postmaster@ and abuse@ email addresses for the main hostname domains on your server. By this I mean set up [email protected] and [email protected].

This will show to Hotmail and the others that you are accepting complaints correctly so that if the people do not wish to receive your emails they will be able to do something about it.

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