Many factors affect email deliverability (the ability for emails to reach the inbox of their intended recipients). Modern mailbox providers, such as Gmail, Yahoo, Hotmail, Outlook, and Microsoft, use proprietary algorithms to analyze hundreds of signals and decide if an email gets rejected, delivered to the inbox, or sent to the spam folder.
A positive sender reputation is essential to good email deliverability. You can develop a positive reputation over time by continuously following email marketing best practices. Email setup and authentication, good data hygiene, and strong user engagement are particularly important. This article covers a number of best practices to follow to maximize your domain’s email deliverability.
In this article
Email collection basics
Although the CAN-SPAM Act is silent on the use of purchased lists, it’s a violation of Iterable’s Anti-Spam Policy to use Iterable services to:
- Verify the email address(es) of any person who hasn't directly and affirmatively consented (opted-in) to receiving email communications from you.
- Validate purchased, rented, or similarly obtained email address from a third party (third party email lists).
- Harvest email addresses or otherwise determine the existence of unknown email addresses.
- Send any electronic mail message or wireless communications to any person who has opted out or otherwise objected to receiving such messages from you or anyone acting on your behalf.
These actions can result in your Iterable account being temporarily or permanently suspended. See the Iterable Anti-Spam Policy for more information.
To send messages to email addresses that you've acquired from a third party, you must be able to prove that all subscribers on the list have given you direct permission to message them.
These practices help with protecting your sender reputation and ensuring that your users receive the emails they need and want to receive.
Data hygiene
The quality of your data plays a critical part in your ability to reach the inbox.
- Your lists should contain minimal amounts of invalid or inactive users.
- Your recipients should be highly engaged with your emails (opening, reading, clicking).
- Your campaigns should generate a minimal amount of spam complaints.
Email acquisition best practices
Good data starts with good acquisition practices.
Obtain informed consent from your subscribers:
- Don’t try to trick people into subscribing by using pre-selected checkboxes.
- Don't force users to subscribe to gain access to a game or content, for example.
- Manage expectations by letting subscribers know what type of emails they can expect from you, and how often.
Avoid bad data from entering your lists:
- Secure all your online web forms to avoid bot abuse.
- Use an “on-the-fly” list validation tool (such as Kickbox) on your web forms. These tools automatically detect invalid email addresses and typos and prompt users to correct them.
- Or, your form can ask subscribers to enter their email address twice and validate that the values match. This reduces the numbers of typos in subscriber emails.
Single vs double opt-in
The best way to get quality data is to use double opt-in. A double opt-in subscription model requires users to click a link in a verification email before adding them to the list.
The extra step can result in fewer sign-ups, however, they also produce lists of verified, valid email addresses for engaged users who want your content. This reduces bounce rates and spam complaints, and improves deliverability.
A single opt-in subscription model allows users to sign up for mailing lists or services by simply filling out a web form, without any email confirmation.
When using a single opt-in subscription model, it‘s a good idea to run your lists through an email verification service (such as Kickbox) before sending. While these services won’t be able to catch every single invalid email address, they greatly reduce the number of invalid addresses that make it onto your lists.
For more information about setting up single and double opt-in subscription processes with Iterable, read Build a Welcome Sequence for New Subscribers.
Manage bounces
There are two types of bounces: hard and soft.
Hard bounces
A hard bounce means that the recipient’s mailbox provider or network provided feedback that this user doesn't exist and that email address can't receive messages.
- These bounces represent a permanent delivery issue.
- Hard bounces can happen when an email address has been misspelled or is no longer in use.
By default, Iterable automatically unsubscribes hard-bounced users from the sending message channel and other channels of the same type. See Email Bounces for more information.
Soft bounces
A soft bounce can happen for a variety of reasons:
- A full mailbox
- Rejected content (such as from a spam filter)
- Out-of-office messages
- Messages that are too big
- No DNS for the receiving server, no detectable reason, etc.
Iterable doesn't automatically unsubscribe users whose emails have soft bounced. To manage soft bounces, use a journey to periodically check for email addresses that have repeatedly bounced over the past 6 months — a sign that an email address is no longer valid or that the user no longer checks their inbox.
Email authentication (SPF, DKIM, DMARC)
During onboarding, Iterable’s implementation team provides you instructions to update your DNS records to enable SPF and DKIM. These email authentication methods help improve deliverability.
We also recommend that you implement DMARC to prevent the spoofing of your domain.
Sender Policy Framework (SPF) checks that incoming mail from a domain comes from an IP address that's authorized by that domain's administrators. It's usually added to a DNS as a text record.
DomainKeys Identified Mail (DKIM) helps detect whether messages were altered while in transit. It's also added to a DNS as a text record.
Domain-based Message Authentication, Reporting and Conformance (DMARC) is an authentication method that specifies how email should be handled by the receiving server. This helps prevent email spoofing and prevents legitimate email from bouncing. It’s worth noting that you should not attempt implementing DMARC until you have a clear understanding of both the process and the mail streams sent on your behalf. For more details, see https://dmarc.org or talk to your customer success manager.
Manage channel and message type subscriptions
With Iterable, you can send emails from multiple message channels. To insulate deliverability concerns and protect sender reputation, it’s a good idea to set up separate message channels that use different IP pools and sending subdomains.
To learn more, read Message Channels and Message Types Overview.
Use dedicated IPs
You can use separate IPs for marketing and transactional email, for example, to isolate deliverability problems. This isolation prevents an impact to the deliverability of your business-critical transactional messages in cases where many users report a marketing message as spam.
Use subdomains for sender addresses
Sending email from a subdomain-based address clearly associates marketing emails with your company's brand, while at the same time isolating them from the sender reputation of your corporate root domain.
Use sub-domains to clearly label your separate mail streams. For example:
- Promotional messages:
deals.example.com - Transactional messages:
info.example.com
In Iterable, you can add several subdomains to send from in a single project when you use your own ESP. To learn more, read Email Setup, or ask your customer success manager for help.
Limit message frequency
Iterable has a built-in rate-limiting feature for marketing channel emails. You can send a single email template ID to the same user only once every 18 hours.
Journeys
Additionally, for a journey you can set a number of allowed simultaneous entries in your start tile to prevent users from entering more than once at a time. This feature is useful for a welcome series or cart abandonment campaign.
Campaign and Data Feed rate limiting (beta)
Iterable's Campaign and Data Feed rate limiting is currently in beta. This feature provides more control over campaign orchestration by setting an upper limit on how many sends and data feeds go out per second/minute for a given campaign. Contact your customer success manager to learn more about this.
Customize the To field
Customizing an email's To field improves deliverability by confirming to ISPs that you know the first and last name of the people to whom you're sending.
To enable this feature, go to Settings > Project Settings. Then, in First Name Field and Last Name Field, specify the Iterable user profile fields that contain the first and last names of your users.
Best practices for sending email
Use an easy-to-recognize sender name and email address. Make sure the sender name and email you use are easily recognizable so that users know the message comes from your company.
Your sending domain should be related to your brand’s website domain. Mailbox providers prefer to see a direct relationship between the domain used for sending the emails and the brand’s main website (for example, if your website is
www.example.com, usemail.example.comfor sending emails).Preheader text should align with your subject line and provide relevant and inviting information.
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Keep messages below 103KB. Gmail clips messages with HTML content greater than 103KB. If your email is too big, the following message appears in your template's preview:
If you use Iterable's device preview, you can see where Gmail clients clip the message, as shown here:
To prevent this from happening, keep emails short and direct. Make sure the email content is easy to read by using high contrast and big enough fonts.
Avoid URL shorteners. Spammers and bad actors often use link shorteners to hide the actual link and direct people to malware and viruses. Because of this, the use of such shorteners could land you on a blocklist.
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Remind users why they receive your messages. It can help users to see an explicit reminder as to why they've received a message. For example:
"You are receiving this email at {{email}} because you signed up for a mailing list on our website."
Ensure that your lists contain valid email addresses. Hard and soft bounces can negatively impact your sender reputation. To minimize them, use a tool such as Kickbox to verify your lists before sending.
Suppress users that repetitively bounce over time. Use Iterable's segmentation tools to identify users who repetitively bounce over a long period of time (6 months or more) and suppress them.
Check your unsubscribe mechanism. Make sure your unsubscribe link works and is visible, and that the unsubscribe process is easy to use. For example, don’t force your users to log into their accounts to change their email preferences.
Maximize engagement
To maintain good deliverability, it’s critical that users positively engage with your emails (opens, clicks, forwards). Their positive engagement demonstrates to mailbox providers that users want to read your emails.
To maximize email open and clicks, consider these ideas:
To increase the likelihood that users receive your emails at times when they're likely to read them, consider their time zones when sending and use Iterable’s Send Time Optimization feature. For more information, read Optimizing Campaign Delivery
Use buttons to highlight the primary calls to action in your messages.
Fill your emails with engaging, useful, appealing content. For example, promotions for products and services can encourage people to interact with your messages.
Less is more. Users are most likely to engage with content that's direct and to-the-point.
Use responsive email templates to ensure correct display on all devices (subject to how well the email client renders the provided HTML).
Consider using AMP for Email to send interactive, app-like messages that help users accomplish meaningful tasks right from their inboxes.
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Remove users who haven’t opened or clicked in a while. How often you do this depends on your business model and mailing frequency. We recommend 6 months, however don't go past 12 months at most.
For example, identify users who haven’t engaged in over 3 months and reduce their sending cadence. If they’re still unengaged, send them a couple of highly engaging reactivation emails. Then, if they still don't engage, suppress them.
For newly opted-in users who haven’t opened or clicked in the first 60-90 days, or after a certain number of emails sent since they opted in, consider removing them from your list or pushing their email addresses into a reengagement journey.
Monitor your reputation
Free postmaster tools from mailbox providers
If you send a lot of email to users in Gmail, Iterable's deliverability experts highly recommended monitoring your reputation with Google Postmaster Tools. This service provides invaluable insights into how Gmail perceives mail from your domain(s): user reported spam rate, IP and domain reputation, authentication, etc. To learn more about how to set up monitoring with Google, read Monitoring Gmail Deliverability with Google Postmaster Tools.
Microsoft Smart Network Data Service (SNDS) provides insights into mail sent from your dedicated IPs to Microsoft's commercial domains (Hotmail, Outlook, Live MSN)—such as number of emails sent and accepted, trap hits, and complaint rate. Note that this tool is a little more complex to interpret.
If sending to Russia, consider using Mail.ru Postmaster. With this service, you can monitor your domain reputation and inbox placement at this major Russian mailbox provider. You can also upload your logo so that it displays in the recipients’ inboxes.
Blocklists
Use tools such as MX Toolbox to ensure that your IPs and domains aren't listed on any impactful block list (like Spamhaus or Spamcop).
Iterable doesn't provide IP reputation monitoring and alerting, but there are various services (such as Validity Everest) that do.
Because Iterable doesn’t have freemium plans and carefully vets new clients, its shared IP address ranges typically have very good sender reputations. As you initially configure your DNS, when using shared IP address ranges it's best to "warm up" your domain, similar to what's required when sending on new dedicated IPs. This means starting with a low volume of mail, sending first to your most engaged recipients, and increasing the volume slowly and methodically.
Inbox placement
It’s impossible to know exactly how many emails get delivered to the inbox vs. the spam folder, because mailbox providers don’t feed back this information.
Monitoring open rates by mailbox providers over time can glean useful insights and help identify a spam placement issue. Keep an eye out for any sudden drop from a particular provider, which could indicate that your emails are getting placed in spam folders.
Seed testing
Seed testing is another way to check inbox placement. To seed test an email, send it to a list of emails that includes many different email services where you can view the message (Gmail, Outlook, Yahoo, etc.). Then, verify that these services accept the message and find where the email was placed (inbox, spam folder).
NOTE
To learn about deliverability services and tools that provide deliverability monitoring and seed testing, contact your customer success manager.
Want to learn more?
For more information about some of the topics in this article, check out this Iterable Academy course. Iterable Academy is open to everyone — you don't need to be an Iterable customer!
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