Deliverability Sessions: Managing Large Volume Spikes in Email

Introduction:
In an ideal world of email deliverability, email is sent on a regular cadence to a normalized lists of subscribers and recipient email addresses with no major changes in pattern. Typically the volume, list members and content are relatively the same and mailbox providers (such as Gmail) begin to expect that schedule and those volumes. Often times however, marketers are tasked with sending out campaigns (both marketing and transactional) with little time to prepare and even less time to ramp up to a normalized schedule. This can create not only a short term deliverability problem but potentially a long term deliverability problem as your sender reputation may suffer as a result of big changes to volume and cadence. This blog provides some recommendations and points to consider that will give your messages a better chance at inbox placement and thus engagement.

What Internet Service Providers (ISP)/Mailbox Providers (MP) Expect:
As email senders, we are responsible to understand and adhere to the recipient domains we are attempting to send messages. For example, if you are sending a good portion of your emails to Gmail or Yahoo you should understand what each mailbox provider expects in terms of warming up, sending throughput, and general deliverability advice. Examples of these resources can be found here for Gmail and Yahoo. The important thing here is that while general email practices are similar, each mailbox provider may have specific requirements or recommendations for delivering to their users. The mailbox providers top priorities are to #1 deliver wanted messages to their users and #2 block unwanted messages from getting to their users. So one of the keys to developing a good approach even with spikes in sending is to understand your destination ISPs/mailboxes and make sure you’re following the recommended best practices from those ISPs/MPs.

Ultimately you need to build trust with the ISPs/MPs in order to successfully deliver to them. A big part of it is understanding what they expect but the following key areas will also provide valuable recommendations for approaching an email program with variant timing and volumes. These topics include: List hygiene, bounce/complaint management, list segmentation/stacking & scheduling, and IP/Domain environment.

List Hygiene and Management:
The next area of focus we’ll review is your list and how you manage your list. It is important to understand that building a list is hard and takes a lot of time and effort but it is important to build your list(s) organically. This means that you only send to folks who have explicitly signed up for whatever it is you’re planning on sending them. The goal here is to honor your user’s preferences and at times limit the volume of messages if they are unresponsive.

When a recipient becomes unresponsive over a longer period of time (say over 1 year) a few things are happening if you continue to send those addresses email. The first thing that happens is that your user engagement goes down as you are not getting opens for any of those messages sent. This can be problematic especially as mailbox providers shift to more machine learning and A.I. driven filtering decisions, like Gmail. The second thing that often happens is if they are ignoring your messages purposefully and you keep sending, at some point they may select all the messages and flag them all as spam inflating your spam feedback numbers. The third thing that happens is that ISPs/MPs start to see lower overall user engagement which then reduces your sender reputation score with them and if your spam rate spikes as well, you’ll be certain to have deliverability issues.

The best way to manage your list is to be as targeted as possible in terms of your brands, offerings, and what the user initially signed up to receive (or implicitly confirmed through a purchase or transaction). Understand that if a user is not engaging with your message it is best to stop sending that specific series and look at putting them into a win-back style campaign in which you make one to a few more attempts to connect with the recipient and confirm their preferences and opt-in status to those mailing lists.

In large volume sending days, you still need to honor previous unsubscribes and spam complaints by removing them from your active mailing lists and not sending to those addresses that have explicitly opted-out. Additionally, large spikes in bounced email addresses (invalid addresses) will also negatively impact your sender reputation so be sure to keep your suppression list(s) and bounce management current.

More information on strategies for list management are available in this SES Blog post:
https://aws.amazon.com/blogs/messaging-and-targeting/strategies-for-list-management-with-amazon-pinpoint-and-amazon-simple-email-service/

IP/Domain Reputation:
Building and maintaining IP and domain reputation is extremely important when it comes to consistent deliverability and also having good enough sender reputation to have a spike in traffic without immediately running into deliverability issues. The best way to maintain good sender reputation (both IP and domain) is getting high user engagement (Unique Open Rate) and low complaints. High user engagement means users are interacting positively with your messages at a high rate, primarily identified by Opens but can also be supported by clicks as well. The rate can vary based on industry but if you’re getting around a 20% unique open rate, you have high user engagement and are doing well with your list. But rates can vary depending on industry, frequency of sends, types of messages and content. Complaints can hurt deliverability quickly because it is instant feedback to ISPs/MPs and if the complaint rate is high enough it is a major trigger for the ISP/MP to react negatively which typically results in putting messages directly into the spam folder, throttling messages (deferring) and/or blocking the message outright.

List Segmenting and Scheduling:
When it comes to a large volume spike in messaging for your email program list segmenting and scheduling is extremely important. Typically you want to avoid a large spike in volume but at times it is mandatory to send out. To do so you need to split out your segments by likely best performance. You want to send to the subscribers that will most likely engage with the message positively – for instance your new signups, recently engaged in a message and long term engagement (multiple opens within the past 30 days for example). This does two things. First it allows the most likely to positively engage with the message the opportunity to get the message to their inbox. The second thing that will happen is that as you get better initial engagement on your first few segments, your sender reputation will continue to improve and the next segments will have a much better chance at also hitting the inbox as a result of good performance from the first segments.

When you need to send a large volume spike, utilize as much of your scheduling flexibility as you have available. If you have 2 days to send the massive spike, use the full two days and spread the segments out. This helps you reduce the size of your message blasts to an ISP/MP. In addition, you can monitor performance of your segments which will start to give you a better idea of where in your list the ROI might not be worth the risk. For example, once you get towards the end of your list it may not be worth sending to people who have never opened a message in the past year and the risk of a complaint, bounce or unsubscribe may outweigh that benefit of a potential open/click.

Authentication:
There are two authentication mechanisms for email which are SPF and DKIM. SPF (Sender Policy Framework) is a simple text record within the DNS of the sending domain that lists the IP addresses that messages should always come from and a policy indicating what to do with messages that are not from those resources. These options can be rejecting a message, accepting all messages or accepting messages but placing them in the spam folder. Additionally DKIM (DomainKeys Identified Mail) is an encrypted signature within the message header to validate the message came from the purported source. Most mailbox providers require both authentication mechanisms to exists to pass the message on to their users.

In additional to these two authentication mechanisms is another reporting mechanism called DMARC (domain-based message authentication, reporting and conformance). DMARC utilizes SPF and DKIM protocols to indicate to recipient mail servers that the messages are protected by SPF and DKIM and how to handle the messages based on the alignment of these two protocols. In addition to creating a delivery policy, DMARC provides the ability for the recipient to send back reports to the sender indicating a pass or fail of the DMARC evaluation. This is a good mechanism for brands to see if their brand is being spoofed by bad actors and/or if they have authentication issues for various sources of their messages.

Authentication is not only suggested but it is required. Passing SPF and DKIM are critical for message delivery. DMARC allows senders to additionally impose policies based on these two heavily used email authentication protocols. DMARC also provides insight into other sources who may be purporting to your brand.

More information on these protocols can be found here:
SPF: https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-authentication-spf.html
DKIM: https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-authentication-dkim.html
DMARC: https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-authentication-dmarc.html

Final Thoughts:
Even though you will sometimes be forced to go off schedule (or possibly a non-normalized schedule is the norm) you must still try to align with ISP/MP best practices when possible. The goal is to build and maintain trust with not only the ISPs and Mailbox Providers but more importantly with your recipients. Your recipients are your key to email deliverability success – send them what they want and honor their opt-outs or preference center updates and you will be on the right track for good email deliverability.