Black Friday, Cyber Monday, and Christmas are just around the corner. For many ESPs, this is the busiest time for sending. For marketers using the ESP, emails must be delivered in a timely and secure manner. However, during this season, bounce messages such as ‘rate limit exceeded’ are increasingly common and seen by senders monitoring their outbound traffic - often a result of a poorly optimized setup. 

In September, we teamed up with the Certified Senders Alliance (CSA) to hear from four email experts who shared their tips and tricks on how to deliver email. During the webinar, we heard from Sidsel Jensen, Architect of Deliverability and Abuse, Open-Xchange; Tam Bond, Head of Messaging Operations, dotdigital; Sebastian Kluth, Technical Lead, Certified Senders Alliance; and our very own Andrew Bonar, Executive Advisor, Halon. 

Here are 5 key takeaways that we learned from our webinar with CSA.

Sidsel said that rate limits do have their justifications, as long as the mailserver’s compute resources are limited and spam levels are high. Rate limiting is an effective component in the toolkit and is seen as a protective shield against abuse. It’s important to keep the mailserver's resilience and availability high so that even in the midst of a service disruption the service levels are acceptable. However, there are no silver bullets or one size fits all scenarios. There are a lot of variables to consider when it comes to rate settings. A good rule of thumb is to start low and turn up the volume of traffic slowly.

Before you even think about rate limitations, you need to make sure you have the right setup and that includes the right infrastructure. Your developers and engineers need to work together with the sales, deliverability and marketing teams, and be aware of any compliance requirements to better understand the environment they are working in. 

Some common housekeeping rules to keep in mind are: 

• What are your practices for the collection of data? 
• How are people managing the data? 
• How are you sending out your emails? Could they be considered spam?

Delivering email is not the same as working with a well-documented API and you will not always get the same error message back and sometimes those error messages may not mean what they seem to say (https://smtpfieldmanual.com/ is a good reference point). It’s important to understand the ecosystem that you are working in and realize that email is not an instant medium. 

Various processes happen to an SMTP transaction and those events result in the email landing in someone’s inbox. Therefore it is crucial to respect the email ecosystem and the networks involved in delivering your message. Warming up your IP slowly and looking at your gradual ramp-up will help mitigate the chance of these issues and increase the likelihood you will be seen as a great sender. As per the famous quote; slow and steady wins the race, and if there is a message that is being deferred, often it’s because of a heavy load and it’s not going to get there any faster by repeatedly banging on the door. 

By looking at your retry intervals, you can prevent your mail delivery attempts looking like DDOS attacks and give signals that you are a good actor in the ecosystem. This will help prove that you are not a spammer and learning the limits of your provider will help you respect their limits and you can optimize mail delivery accordingly. 

4. Test, Test, Test

According to dotdigital, 600 million emails were sent on the Black Friday, Cyber Monday weekend in 2021 which was 37% higher than in 2020. There is big money to be made from this large volume of email traffic and testing campaigns are critical to their success. 

When it comes to testing, Tam states that there needs to be a scientific methodology and remember when testing, tweak one variable at a time only when working towards the optimal settings for your setup and user base. Andrew mentions that as a sender, you need to be looking at the data available in your MTA logs and using Elastic, Kibana or similar to get actionable reporting to gain insights into what is and is not working during your testing phase.

5. Optimization is key 

Sidsel believes that less is more when it comes to email campaigns and if senders can optimize their newsletters, it will be easier for mailbox providers. She suggests optimizing for mobile first, segmenting customers and personalizing emails as much as possible rather than sending out blanket email templates. Sidsel also recommends that senders should not send at the top of the hour.

“As a mailbox provider, it is helpful to tell senders to schedule their email campaigns across the hour.”

There are many trends and variables that need to be considered such as the time and day of the week of your send. For example, an email campaign sent on Tuesday morning will yield different results than a campaign sent on Friday afternoon. 

Tam mentions that dotdigital technically scales up its platform. They make sure they have CPU available, sufficient storage for spooling, and are always improving their settings that help senders customize and personalize their email campaigns. “We do a post-mortem of the season to see if we need to do more warm-ups of IPs to handle different connections”. Tam suggests that a good time of year to start warming up your IP is August to give you three months to prepare for the email season. 

Want to hear more about rate limitations and how you can prepare for the email season? Click here to access the CSA webinar.