With crowded consumer and business inboxes, email deliverability and inbox placement has become a top priority for marketers in recent years. Getting emails flagged as spam or blocked by mailbox provider has an impact on sender reputation and future inbox placement.

Many marketers use “deliverability” as an equivalent to “inbox placement,” but the terms are not the same. Emails that go into Spam folder are considered delivered, where is marketer’s goal is to ultimately get emails into subscriber’s inbox.

The major factors that affect deliverability are:

  1. Global engagement (overtime, across campaigns)
  2. Content and format of the email (spam words in subject or message body, format – use of images, etc)
  3. Relative engagement for you (sender) versus other senders in the recipients inbox
  4. IP reputation
  5. Sender reputation (e.g. sender being your domain or exact email address the emails are sent from)
  6. Server and domain configuration (DKIM, SPF, etc)

email deliverability factors

Email deliverability factors

On the diagram above, the green box represents factors that vary and change more with each campaign sent and the square on the left with 4 factors are not subject to dramatic changes on a per campaign basis. In this guide, we are covering 5 out of 6 factors, but you can learn more about IP reputation management here.

The list of best practices below can help you achieve better email deliverability from building and maintaining a strong sender reputation, while improving your engagement. 

Global engagement – keep bounce rate low

An average email list decays at a rate of 2% per month for B2C lists and 3% for B2B lists. The rate is higher for B2B lists because people change work emails more frequently than personal emails, due to job changes. So if you haven’t engaged with your email list for more than 6 months you are likely to have a more than a 10% bounce rate on your first bulk campaign. A bounce rate over 10% can get your account suspended with many email service providers (ESPs), but it also has a negative impact on your email deliverability and sender reputation, not to mention cost (since you pay to send email to invalid addresses). Inbox providers pay close attention to bounce rate and may block emails from a sender that attempts to deliver to invalid email addresses.

At BigMailer, a bulk campaign with a bounce rate over 8% (default, configurable by customer) is automatically paused to protect sender reputation.

Old and unengaged lists should be validated before being imported into an email marketing platform. Most email validation providers recommend that you validate your entire list once a month, or before every campaign you send, to keep your bounce rate as low as possible. While that tactic can be pricey, the good news is that most email validation providers offer great volume discounts for purchasing credits in bulk (that usually never expire).

We have partnered with low-cost email validation services Bouncer (GDPR compliant, recommended for customers in Europe) and TheChecker to get our customers a discount on their services.

Email content and format (including email headers and links)

1. Use a custom tracking URL in your emails

Using a custom tracking URL in your emails can help your emails appear more authentic and help with inbox placement. Consider customizing tracking URL for your emails, using the same domain as your sender address. For example, if your sender is sales@your-domain.com you can use email.your-domain.com as your tracking URL.

custom tracking URL

Examples of commonly used tracking sub-domains

This will require updating your domain’s DNS records (to create that email subdomain and map to email provider servers) and then adding the updated records to your email provider’s platform as a configuration or setting. Most market leaders allow this, although some call it white labeling and most charge extra for it or make it available on higher tier plans. 

2. Create a plain-text version of your email

While only a tiny fraction of your audience may see the value in a plain-text email, SpamAssasin, a widely used spam tool, considers it essential. The tool assigns two points to your email if no plain-text version is available. If your message reaches a score of seven, it’s identified as spam, so two points is a pretty big penalty for something that’s fairly easy for a savvy marketer to execute.

While some email platforms (like BigMailer) will auto-generate a plain-text version from the HTML version, most of them don’t require one. If you have to create a plain-text version yourself, don’t cut corners – it should match the message in the HTML version and not be any shorter. Check out this article from Litmus for more guidance on formatting plain-text emails.

3. Make it easy to unsubscribe

Making it super easy for users to unsubscribe is not a tactic that’s obvious to benefit the sender, but it is. If email recipients can’t easily locate the unsubscribe link they are likely to hit the Spam/Complaint button instead. Complaint is the worst type of engagement for your email campaigns. 

Your unsubscribe or “subscription preferences” link needs to allow a user to either opt-out from your brand communications or  select the message types they want to receive (see the example below) and not to a page that requires them to log in to their account to retrieve or save their preferences. The latter has become a more prevalent practice among some high profile brands that use their own built-in-house email tools. This practice is actually in conflict with anti-spam laws. It’s advisable to provide users with a straightforward method for getting off an email list and honor that request in a timely manner.

It may be helpful to offer subscribers a way to opt out from certain communications instead of all brand communications at once. Providing this option has become even more necessary with the introduction of General Data Protection Regulation (GDPR) laws in May 2018, which states that the consent to receive emails should be explicit and not be bundled (e.g., if subscribers only opted in to receiving product updates, you can’t additionally send them promotional emails or messages on behalf of your partners).

Example: unsubscribe page with preferences format

Example: BigMailer.io unsubscribe page with preferences format

4. Specify a useful sender (from) address

Be it a question or general feedback, email recipients commonly want to respond to the messages they receive. For this reason, it’s best if your reply-to email address is one that goes straight to your support team (or at least forwards to them). You don’t want to discourage your subscribers from responding to your message by using a no-reply address, such as noreply@your-domain.com, because replies are part of the engagement metrics that some email service providers (Gmail, for example) use for determining the importance of your email and whether it belongs in the inbox or spam folder.

Another consideration is that customers will sometimes request removal from a mailing list, and if they see noreply@your-domain.com they are more likely to hit the “Spam” or “Complain” buttons instead – complaints are the worst form of engagement you can have on your email campaigns.

Lastly, no-reply addresses run a greater risk of being sent automatically to the junk folder. As this GlockApps article states, “Some ISPs, network spam filters, and customers’ personal email security settings are set up to move messages with ‘no-reply’ addresses to the junk folder.

In short, if you care about your email campaigns’ engagement rate and future deliverability, specify a meaningful sender address for and avoid using a no-reply email address.

5. Use a descriptive Sender label

While a clever subject line can certainly help you stand out in a crowded inbox, your subscribers will still need to recognize your brand’s communication when they scan their inbox. You don’t want them left wondering why they’re getting an email from someone they don’t know with a cryptic subject line that promises to solve pain point XYZ.

Consider these three basic options for sender labels:

  1. Brand or Product Name
  2. Brand or Product Name + Function (e.g., Support, Sales)
  3. First Name at/from [Brand or Product Name]

With the third option, consider the name of the person as well as your product name. Is your product name a single word, one to two words or longer? Will the entire label fit in the “From” field? Whatever format you choose, make sure to be consistent across all of your sender accounts and test for appearance before you start using a new sender label.

6. Use preview (aka preheader) text

While it isn’t always a visible element of your email’s design, preview text provides valuable real estate to expand your message. You should think of it as a second subject line – an additional opportunity to convince your recipients to open your email. The better your open and engagement rates are, the better chance you have of landing in the inbox. Many platforms, including BigMailer, support specifying this text. If your platform doesn’t support it, you can still have a preheader element as part of your email template design.

7. Test emails with spam tools

Testing every email adds an extra step, but it’s an incredibly important one. Because testing typically has to happen outside of an email marketing platform using tools provided by websites like Litmus, Email on Acid or GlockApps, you may be tempted to skip it. You shouldn’t – it may mean the difference between your message being successfully delivered or it being flagged as spam.

With that said, even experienced marketers using these tools can’t avoid landing an email in the spam folder every once in a while – this is especially true for Gmail and is often due to the topic of the message.

Starbucks email in spam folder

Example of a high-quality email and sender in spam folder

Don’t stress – if the occasional email gets a low engagement rate because a few spam keywords made it into your message, know that you are not alone. It’s become necessary at this point for email marketing platforms to embed email testing into their platforms to simplify a marketer’s campaign workflow. This is exactly what the team at BigMailer is currently working on, and we hope to delight our customers with this workflow improvement soon.

Relative engagement

Mailbox providers keep track of how your email recipients interact with your emails, so you need to maintain a high engagement to achieve a high inbox placement rate. Consider these tactics:

  1. Periodically remove unengaged subscribers from your list. Identify anyone who hasn’t engaged with (didn’t open) your emails for 90 or 120 days and either permanently remove them, or exclude them from your frequent mailings (you could send them your highest engagement/appeal content or only critical service notifications regarding their accounts).
  2. Send emails with appealing call-to-actions (CTAs) and make it necessary to click and interact with your email. It may seem obvious, but it’s not uncommon for some marketers to include phone numbers to place orders or have the website address in giant font to make it memorable, which may push a user to simply type the address when they are ready to place an order instead of clicking on a link in an email (and for a marketer to correctly attribute a conversion or sale to the email sent).
  3. Engage in email exchanges with your customers using the same email address that you use to send emails, or at least using the same sender domain, for example for customer service inquiries. Any email interactions between your and your customers signal trust to mailbox providers.

Consider using a dedicated IP address

IP (internet protocol) address is a unique address that identifies a device (computer or server) on the Internet or a local network. When you start using a hosted transactional or bulk email marketing service, by default, your emails are being sent from a group of servers with different IP addresses, and that group of servers is shared by multiple senders like you. So your emails use a “shared IP pool” and the reputation of those shared IP addresses is shared as well.

The biggest factor in IP reputation is whether it’s blacklisted, which happens when emails sent from a given IP get flagged as “Spam” by the recipients. If the % of complaints is high enough, the IP gets blacklisted and may get blocked by ISPs.

You can benefit from a dedicated IP address IF:

  • You are looking for a fresh start and looking to invest in building a strong email sender reputation
  • You have a small list now, but plan to grow it fast and monetize it, while controlling cost and ROI by using a low cost provider
  • You have built up a sizable list (over 20,000 subscribers) and ready to engage it with high quality content

Unfortunately, low volume senders are limited in their options because most low cost bulk email marketing service providers don’t offer an option to get a dedicated IP address on lower pricing tiers. And if you use an ESP that does offer access to a dedicated IP, it may come with a hefty price tag (for example $250 per IP at ConvertKit). If you use an ESP that runs on Amazon SES, like BigMailer, you can request a dedicated IP(s) from Amazon anytime, at a cost of $25 per IP per month.

Manage sender reputation – keep complaint rate low

Just like with an IP reputation, the sender reputation is affected by email recipients marking the emails as “Spam”. An industry benchmark is to keep complaint rate below 0.1%, but it’s more nuanced than that. The lower the volume of sending the less sensitive a mailbox provider is to the complaint rate, due to statistical insignificance (just 1 complaint can change the ratio dramatically). High volume senders have to be more vigilant – being close to the 0.1% ratio can trigger a manual campaign review from an ESP they use and can be followed by an account suspension.

A site/domain can also be blacklisted as unsafe with various monitoring services, like Google Save Browsing. You can monitor your domain/IP health by signing up with various providers, like Google Postmasters, or blacklist monitoring services.

Manage your sender domain identity

While this step is optional with most email service providers and requires a little more technical knowledge than the other items in this guide, most email platforms allow you to configure Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) for your domain to help improve your sender reputation by making it appear more authentic and safe. We highly recommend getting both SPF and DKIM configured for every sender domain you use to send emails. 

Use a different sender domain and IP addresses for any cold email campaigns, which have the lowest engagement and can burn your sender reputation. You may want to consider using a different sender identity for your marketing and transactional emails as well, to ensure your transactional email delivery doesn’t get affected by your bulk campaign practices.

Did you find this article helpful? Were you able to find a few useful practices to include in your email campaigns? Please leave a comment – I would love to hear from you.