Deliverability

Complete Guide to Email Deliverability

  • 21 October 2022
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Messaging is the lifeblood of your business. The Customer.io Customer Success Team wants to help you improve and take control over your email deliverability in 2022 and beyond so that you can always ensure each message has the most impact! This article is a complete guide to all things email deliverability. 

 

Domain & IP Reputation 

 

One of the most important assets you have in the email world is your reputation. This is made up of your sending IPs & domain. A good analogy for your email reputation is your personal credit score. Obviously, a bad reputation will hurt you. However, not having a reputation will also hurt you. If ESPs don’t know you (or more specifically your IP and domain) they will assume the worst and slow down delivery, reject, or filter your messages to spam. It’s tough to blame them given all the spam out there. Due to the importance of reputation, a significant portion of our discussion on best practices revolves around building and maintaining your email reputation.

 

There are lots of 3rd party vendors who make large promises on 'fixing' your deliverability to magically get your emails to the inbox. This is most definitely not the case as your actions, as the email sender, play the biggest part in good deliverability. 

 

A low IP or domain reputation is the most common reason that a given email might be filtered to spam. Customer.io manages and maintains the IP reputation of its shared IPs and ensures that all email sent from our network meets all required technical requirements.You can also monitor your domain & IP using a 3rd party service. We highly recommend Google Postmaster Tools. As Gmail is the most utilized inbox provider in the industry and represents the vast majority of your recipient pool, keeping track of your Gmail specific reputation is a critical step to take.

 

The number one reason we see customers get blocked or suffer reputation damage is due to poor mailing list health. Sometimes the issue is obvious (like purchasing lists - a BIG no no) & other times it is just because your mailing list is missing regular maintenance. Here is how to audit your current email list. 

 

 

What to look for in your list health

 

Recipient Engagement 

Blasting every person who ever provided an email is a quick way to lower your reputation. Emailing is the same as building a relationship - you want to send content that is relevant & engaging to customers. (more specifics on email content below 😉).

 

Customers tell you the content is relevant by opening emails & clicking on links. Include filters in your Trigger segments to hone in sending to those customers who engage. An engagement segment can include conditions like 'did click on any tracked link' or 'did open any email in the last 120 days'. We suggest using a time constraint of about 4 months to capture engaged profiles. 

 

Sunset Policy 

Sometimes customers sign up & then in the future no longer want to engage. You can attempt to re-engage these profiles with a specific campaign, but if they still don't respond, it's time to take them off your mailing list. A good place to start is 6 months - if a customer has not opened an email within the last 6 months then it may be time to unsubscribe or delete their profile. Industry-specific engagement criteria will vary from business to business so the exact sunset criteria you adopt is entirely up to you (we have a recommendation here), however no email should ever be sent to a recipient who has not been sent any email in greater than one year. The goal here is to ensure that you have established a plan for removing recipients from your lists if they don’t engage or respond to re-engagement attempts. 

  

Double Opt-In 

This is the one most likely to get a response of "I don't wanna!" & trust us, we get it. The potential downside is that you end up with less people on your email list if they do not complete the double opt-in...BUT the upside is that every person on that list now has confirmed & shouted from the roof top that they want to get emails from you. This is a sure way to guard against spam complaints, bounces, & other deliverability issues. 

 

Check Your Forms 

Picture this - a malicious bot lands on your site & spam bombs your sign-up form. Seconds later thousands (or hundreds of thousands) of emails are sent out to nonexistent or spam tramp emails. The result - your domain is tanked & now you have to spend the next few months in triage rebuilding your reputation. We have seen this happen to customers, but it doesn't have to happen to you! Fortunately, there is a way to guard yourself against these types of attacks - add a reCatpcha to every form on your site that is not behind a sign-in or paywall. This may take your engineering team a bit of extra time, but will save your marketing efforts in the future. Google has a great free resource for this as well. 

 

Why Limits can help your deliverability

 

Data-Driven Sending

Beyond engagement, your business probably gathers & stores other information on your customers: their interests in specific products or services, location details, past purchases, & activity on your site to include a few. These details can be included in trigger segments or campaign branches to further narrow down your audience & send out targeted information. For example, if you send event information to Customer.io when your customers make a purchase, you can use the event data to send targeted follow-up emails for future products. This type of filtering will be more likely to ensure a high reputation as your customers engage with the content. 

 

Sending Volume & Re-engagement  

There are two instances when volume can impact your deliverability - a sudden spike in sending & when sending to unengaged contacts. 

 

For best deliverability, your sending rate should remain steady over time. If you take a look at your weekly & monthly sends, ideally the trend would be shallow, rolling waves as opposed to deep valley & tall peaks. If you are wanting to ramp up sending or are preparing to deliver a message to a larger than normal section of your audience, using rate limiting or branching with time delays can help ensure that the deliverability remains high. 

 

Additionally, if you have a segment of unengaged profiles that you would like to re-engage once more before permanently unsubscribing or removing from your account, using a rate limit can help ensure that you can safely reach out to these new prospects. Before re-engaging these profiles, be sure to have a conversation with your CSM about how to approach messaging. 

 

We have gone over a lot of best practices around sending messages & to whom, but the content of your emails can also contribute to your messages reaching your customer's inbox.

 

 

Email Content 

 

 Here are our best practices for high delivery emails: 

  • Personalize emails to each recipient using Liquid. Ideally, the content should reflect the recipient’s specific interests or usage patterns in your application. 
  • It is best to send multi-part emails using both text & images or text only. Sending image only emails is generally not well received by ESPs. There are a few tools available to test how your email will render across ESPs and browsers. Litmus offers one, as does Return Path.
  • Too many links and images trigger spam flags at ESPs. The higher the text to link and text to image ratios, the better.
  • Misspellings, spammy words (buy now!, Free!) are big spam flags. As are ALL CAPS AND EXCLAMATION MARKS!!!!!!!!!!!!!
  • Use unsubscribe links. Either the Customer.io native global unsubscribe or a custom unsubscribe url.
  • Links should include the domain that is sending the email & avoid link shorteners. The majority of the links in your email should match the sending domain as opposed to linking to a 3rd party site as this is considered a spammy practice by many inbox providers. Also, popular url shorteners can be a bad idea because they are frequently used by spammers.
  • A/B test your emails to optimize recipient engagement. Subject lines are particularly important.
  • Lastly, the domains in the from field, return-path and message-id should match the domain you are sending from.

**The landscape of email deliverability has changed a lot in the last few years. While your email content is still factor to a certain extent, inbox providers heavily weigh your individual sender reputation when analyzing the content of a given message. Content scanning is primarily designed to identify phishing attempts or other unwanted emails.

 

Use the Message Library to audit your active emails & ensure they meet the best practices listed above. 

 

 

Metrics to Monitor  

 

We mentioned signing up for Google Postmaster Tools to monitor your domain & IP reputation, but there are other metrics within Customer.io to keep an eye on too. These metrics below can give you insight into your engagement & overall efforts. 

 

Open Rate 

While open rate is becoming a metric of the past (due to Apple mail relay and pixel blocking) it's still safe to consider a baseline open rate of 20% as a signal that the majority of your messages have landed in the inbox. A sub 20% open rate on a single message or broadcast doesn't indicate an inbox placement issue, but a rolling open rate below 20% is worthy of concern.

 

Spam Rate 

Ideally this number will be 0, but it is natural for a small number of customers to mark an email as spam. Anything over .10% indicates a problem with the type of messages or your list health & should be addressed immediately. 

 

Bonus: Profile Growth 

While not a key indicator of deliverability, understanding your profile growth over time can come in handy down the road to identify audiences that joined at specific times or when troubleshooting any issues that may arise regarding your data integrations.

 

The ‘created_at’ attribute is highly recommended by our Customer Success team. This attribute should be sent in UNIX format and reflect when the profile was created in your database

 

WHEW! You made it all the way through. Cheers to excellent deliverability! 


2 replies

Thank you for this guide! So useful!

Ignore me - I figured it out.

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