How can I improve the deliverability of my emails?

Last updated: September 27, 2016

Available For:

Product: HubSpot Marketing
Subscription: Basic, Professional, & Enterprise

Delivering to your contacts' inboxes is necessary to be successful at email marketing. If you can’t get into your contacts' inboxes, you simply can’t be successful at marketing via email. Read on for a glossary of email deliverability terms as well as best practices to ensure proper inbox placement.


First and foremost, here's a brief list of email deliverability terms you'll want to be familiar with as an email marketer:

Abandoned Address - an email address that was once an active, valid address but has since been closed out.

Authentication - a way for your recipient's server to verify you are who you say you are as a sender using a domain’s DNS records.

Feedback Loop - the conversation between the sending and receiving servers (i.e. tells us when an email has been delivered, opened, or marked as spam. Also tells us the failure reason for a hard bounced message). It is important to note that not every ISP provides spam complaint reports in the feedback loop. What this means to you is that whatever number of spam complaints you see reported is only part of the story; there are likely more complaints behind the scenes that we just can’t see.

Hard Bounce - an email you attempted to send was denied from or incapable of delivery. This could be due to a variety of reasons such as the address being invalid or the spam filter flagging your content as spammy. For more information on bounces, check out this article

Inbox Placement Issues - difficulty having your mail delivered to your recipients' inboxes. This may come in the form of delivery to the spam folder or outright refusal to accept the message (dropping the message as a hard bounce).

Industry Acceptable Threshold - commonly accepted rates across the email industry as a whole, set by each individual ISP, related to hard bounce and spam complaint rates. When exceeding these thresholds, you are much more likely to experience inbox placement issues due to a compromised sender reputation. The threshold for hard bounces and spam complaints is 5% and 0.1%, respectively.

ISP or Inbox Service Provider - Not to be confused with Internet Service Provider, this is the email service your recipient is using to receive email (i.e. Yahoo, GMail, Verizon, etc.).

Sender Reputation - your reputation encompasses almost every single thing that happens to your message once you hit send. Examples include open rates, clickthrough rates, spam reports and high bounce rates. A really healthy reputation is much more likely to guarantee you entrance to your recipient's inbox. As your reputation declines, however, your recipient's spam filter may choose to route your subsequent mailings to the spam folder, or worse, deny it completely and drop it as a hard bounce due to a poor reputation.

SPAM Complaint - when a recipient has told their ISP that a message of yours is spam. Spam complaints are weighted very heavily against your sender reputation because a complaint requires the inbox owner to actively click on the ‘report spam’ button rather than choosing to unsubscribe.

SPAM Filter - application the recipient’s server is using to screen messages and determine the reputation and legitimacy of the sender and content.

SPAM Folder - (also known as the junk folder) where your mail may end up with poor sending practices / poor reputation.

SPAMTRAP - there are many types of spamtraps. One of the most common types of a spamtrap is an abandoned email address that was reclaimed by the ISP solely to catch spammers / bad senders. Hitting these addresses can sink your reputation as well as cause your domain and/or sending IP to be blacklisted.

Best Practices

Next, let’s dig into commonly accepted best practices:

Stop buying, renting, borrowing or scraping lists

This falls in line with building a relationship on trust. Buying a “confirmed opt-in” list does not constitute an explicit opt-in from those contacts! They didn’t give you permission unless they gave you permission. Without explicit opt-in, an email from you is invasive and intrusive of their privacy, is not a good way to establish a relationship between you and those contacts, and definitely does not inspire confidence or trust in your brand.

Good rule of thumb here is that the first line of communication and/or introduction to your brand should not be via email. When was the last time you received an email from a company you didn’t know and opened it up or engaged in any positive way with it? Your email showing up unexpectedly in a recipient's inbox creates a bad first impression.

In addition to building a bad rapport with these contacts, you risk harming your sender reputation. High bounce rates, having your messages marked as spam, and hitting spamtraps are all very real possibilities when attempting to engage with these types of lists. You’re also unlikely to see a high ROI come from lists acquired in these ways. Also of note, reputable ESPs will not allow their senders to send mail to third party lists, which is usually outlined in their Acceptable Use Policy or Terms of Service. 

Use an opt-out/suppression list

If you have recently changed email service providers, make sure that you download a list of opted-out and hard bounced contacts from the previous ESP. Upload that to your new ESP to ensure you don’t accidentally mail contacts who already specified they no longer wish to receive your mail, or are known bad addresses. This will help for a smoother transition between ESPs and protect your reputation from complaints and hard bounces.

Build a relationship on trust

This starts with only emailing contacts who gave you explicit permission to do so and setting the expectations right up front. This is so important and so easy to do! When you are explicitly clear during the opt-in process regarding what the subscriber will receive (content / value), how often they will receive it (frequency) and sometimes even specifying when, or at least when to expect the very first message (beginning of the month? Every other Monday? etc), your contact is fully prepared when they start receiving mail from you. There is no confusion or surprise when a message from you shows up in their inbox, and, even better, they may be looking for your message (so if it doesn’t show up when expected, they may check their spam folder to find it).

Enable Double Opt-in

Double opt-in requires a new subscriber to confirm their subscription status through the first email sent. If they don’t click on the CTA in the confirmation email, they won’t receive any mail beyond that first message. While this may slow down your list growth rate some, the reality here is that the contacts who follow through with double opt-in really want your mail! You are going to build a list of much more qualified leads that are more likely to lead you to a return on your investment of time spent marketing to them. Additionally, contacts added this way tend to be more engaged on average, than contacts added through the single opt-in process.

Put the choice to subscribe in your visitors' hands

Requiring visitors to opt-in to your emails in order to get a free offer can cause all sorts of issues. You may see fake address submissions to get the free content and avoid the subscription. You may also see spam complaints from contacts who gave their real address because they wanted the offer, but not the email subscription that was required with it. These are not contacts you want in your list of highly qualified contacts.

Vanity metrics don’t make you money, but can cost you big time between paying for those contacts, paying to market to those contacts and having compromised deliverability due to a declining reputation (potentially caused by low engagement, high complaint rates and high bounce rates). They are also skewing your metrics, stopping you from getting a clear picture of your engaged subscriber-base.

Make subscribing to email optional when a contact provides their email address on a form, throw in a checkbox (and pro-tip, don’t make it automatically checked) so they have the power to decide if they want to subscribe or not. You may have less subscribers opting in, but rest assured those who take the time to check the box to opt in are far more likely to be qualified leads and worth your time and effort to market to.

Alternatively, you could set the form up so that a valid email address is necessary to get that content. As in, you either email them a link to the content (so it’s not on the thank you page) or the content arrives right in that email. You will want to make it very clear that it works that way to ensure that people filling out the form give you their real address. This will discourage false address submissions. Even if you decide to go this route, you should still make subscribing optional (so theoretically they could receive the content at their real email address but would not receive anything beyond that, ever, without specifying otherwise on another form).

... And then give subscribers complete control

Let them choose what they receive, how often they receive, and maybe even when. When you put control in their hands, you’ll have a much happier subscriber base and will retain more contacts than not. Contacts may choose to receive less frequent mailings, but still stay subscribed, as opposed to opting out entirely simply because that’s their only option if they’re being overwhelmed by your mailings.

Periodically remove unengaged contacts

Unengaged recipients are holding you back. Not only are you paying to market to contacts who aren’t giving you anything in return, they are actually hurting your ability to deliver email to contacts who want to hear from you. Choose a timeframe (6+ months to be more aggressive, 12+ months otherwise) and when a contact hasn’t opened or clicked on an email of yours in that timeframe, segment them off into a smart list and use the list as an exclusion list moving forward. If they re-engage after they have been segmented off, they’ll automatically be removed from the smart list and available to email once again.

Segment your lists & personalize

Not all of your contacts are interested in the same thing. “Listen” to what they’re interested in. What are they clicking on? What email types do they usually open or not open? Send them more of what they love (and reward them for being loyal!) and they’ll show you more love. More engagement = more likely to get into contacts' inboxes = best chance of success with email marketing.

Personalize your messages. Make your contacts feel special, like you are emailing them and not just mass blasting a list. The more human approach makes contacts feel more connected to your brand/business, like they are actually somebody to you and your business and not just ‘or current resident.’

Send a welcome/thank-you email

These types of email typically see the highest open rates of any other email you send. Generally they are sent within moments of form submission and especially if you set the expectations when that first message will arrive, you should see extremely high open rates on this message. That’s great for your sender reputation and for establishing brand recognition as you begin showing up in their inbox. Also, if you did end up in their spam folder and they know to expect a message from you, they may go looking for that message when it doesn’t show up as promised. If they find and proceed to move the message to their inbox, this teaches their inbox that your mail is valid, legitimate mail that they want to receive and gives a nice boost to your sender reputation.

Be consistent

Have a plan for a consistent mailing strategy. At a bare minimum, you want to get into your contacts' inboxes at least once every few months. This inbox "face time" will do a few things for you:

  • Keep your business fresh in the mind of the inbox owner - this will minimize the chance that they forget who you are and why you’re emailing them (which can lead to higher complaint rates).
  • Catch abandoned addresses quicker so the overall number is never too high (and putting your reputation and ability to deliver to the inbox at risk).

Add a second unsubscribe link

Throwing in a second unsubscribe link at the top of your message goes a long way in deterring what we refer to in the email industry as a "lazy unsubscribe." This is when an inbox owner doesn't want to scroll to the bottom of the message to search for your unsubscribe link so they mark the message as spam, knowing it will effectively work the same way (for them, not for you). You don’t want your contacts to have to jump through any hoops to stop receiving mail from you.

Don't obscure links

Using link shorteners increases the likelihood of your mail being filtered. Due to spammers abusing services like to hide the malicious destination a link would take the recipient to, spam filters largely became wary of accepting mail containing such links into their clients inboxes. Additionally, when using links tied to other domains, you’re assuming whatever reputation is tied to that domain, i.e. if malicious senders frequently send links to, spam filters will eventually pick up on this and filter their mail out, as well as anyone else using these links, even if your own domain reputation is really healthy.

Maintain your sender/domain reputation

Your sender reputation is paramount for maximum inbox delivery. As your sender reputation declines, so does your ability to successfully reach your recipients' inboxes. The lower it goes, the less likely you are to make it into the inbox. Instead, your mail will start seeing delivery to the spam folder, and may even be hard bounced due to a poor reputation. Your sender reputation will follow you from ESP to ESP; thus, it is extremely important to have and maintain a good reputation.

List Hygiene & Engagement

This is so important for several reasons. Not only does high engagement indicate that your subscribers like what you’re sending and are interested in your brand / product offerings, it also has the added benefit of padding your sender reputation. Additionally, when you have high open rates, your recipient's ISP learns that you send legitimate mail that your recipients want to receive and like.


HubSpot covers SPF on your marketing emails since we are routing your marketing messages through our IP addresses. DKIM, on the other hand, is another story. While it is not required to have DKIM set up, it can be the difference between your recipient's spam filter accepting your message or not. It is an added layer of authentication that makes you as a sender look more trustworthy and reputable. Learn how to set up DKIM in HubSpot here.

Offer a different communication method

If a contact is ready to unsubscribe, they might love your content but be looking for a way to declutter their inbox. Give them other options for communication, like SMS, RSS, your social media networks, your company blog, etc.

Make sure your emails don't load slowly

Previewing your emails and testing the reading experience should be part of your regular routine because it plays a huge role in the success of your email campaigns. Don't include images that are too large or elements that don't render well on mobile devices. For more information on email design and content best practices, check out this article

Look for signs of Inbox Placement Issues

Poor engagement, high bounce rates and high complaint rates can compound over time. As they drive your reputation down, you are likely to experience inbox placement issues in the way of delivery to the spam folder over the inbox and hard bounces due to temporary failures. When this starts to happen, it further impacts your reputation causing it to happen more often.

So how do you figure out if this is happening to you? Keep a close eye on your open rates and bounce rates. If your open rates start to go down, that might be an indicator that your mail is being bucketed in the spam folder. As long as the recipients server accepts the message, regardless of where it ultimately places it (inbox or spam folder), it looks like a successful delivery on our side. If your mail is ending up in the spam folder, the reality is that those recipients are very likely NOT seeing that message to open it, which makes sense that open rates would suffer.

Alternatively, if lists you mail normally email to start to see higher bounce rates than what you’re used to seeing, that might indicate your mail is being denied altogether and dropped as a hard bounce due to a temporary failure.

Take the feedback.

Despite all of this hard work, some people will still unsubscribe from your emails. Take the opportunity to solicit feedback from your contacts and then act on it. You may notice trends on your own, like people unsubscribing more frequently from offer emails versus blog emails. Maybe your blog content is great, but your promotions aren't enticing enough to get people to act. Soliciting feedback from unsubscribes won't help you save that email recipient, but it will help you prevent future unsubscribes.