What Developers Must Know About Transactional Emails

Transactional emails are a major part of the user experience. The success of your app depends on happy users, and that’s why this topic is important – you need to make sure you have mastered crafting and sending those messages. 

Since you work with your application infrastructure management, it is most likely that you have already taken care of creating proper workflows and enhancing security. 

Let’s talk about the marketing side of transactional emails. Sending an email to confirm the account creation, for example, sounds so simple. But there are actually so many intricacies! 

IT and engineering roles are nearly 50% responsible for the sending of transactional messages.

SparkPost report

In most cases, developers treat transactional messages like technical notifications. This would make marketers’ hair curl – the transactional emails have sales and branding power. They get 8x more opens and clicks than marketing messages, for a simple reason: their recipients are waiting to receive them.

Try to think like your users. Compare:

transactional message - payment failed-bad example


transactional message - payment failed - good example

In general, there are three main points you should take care of:

  • deliverability
  • email content
  • testing

We have published numerous articles and guides about transactional emails on our blog. This article provides brief and essential information for developers, with a list of detailed articles on every point.

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Deliverability and spam rate 

Have you ever requested to reset your password? You expected the immediate email confirmation, didn’t you? One of the most important things in transactional emails/notifications is getting them delivered quickly. They should also land in the main inbox, not in the spam folder. 

Usually, marketing emails tend to be recognized as spam, but you should also follow a list of rules for transactional messages. 

  1. Domain reputation. To keep it clean, send messages to verified emails only, follow your users’ responses (spam complaints) and the rules we list later on.
  2. IP reputation. Choose your email sending provider wisely, use the dedicated IP for high email volumes, and warm up new IP addresses. 
  3. Domain authentication. There are three main standards: DKIM, SPF, and DMARC. It is reliable to use all of them at once. 
  4. Spam triggers. Spam filters respond to the message content. We will explain the details in the following section of this article. 

Further reading

Email content

The proper email content is essential in terms of both user experience and spam rate. Let’s go from top to bottom. 

Email branding 

Email branding is important for your users. When you receive a message, you should be able to quickly recognize who sent it. Emails should be associated with your company: the clear sender’s name and company logo are already enough. 

Recently, a new authentication standard has been introduced, which also plays a role in branding. It is BIMI, Brand Indicator for Message Identification. It helps prevent spoofing but also enables your logo to be displayed in the inboxes, next to the sender’s name. 

BIMI authentication - logo displayed in an inbox

Headers and subject

In the “From” header use the name associated with your brand, such as the company name. Avoid “no-reply” email addresses, as they not only may confuse recipients but can also trigger spam filters. 

Don’t add many addresses to the Bcc field (this is not a regular reader, but it is worth mentioning here). This also can be treated as spam.

Email subject is also underestimated. Many developers treat it as something important for marketing emails only. It’s true that in marketing emails, the subject line determines whether a promotional message will be opened or not. But for transactional emails, the subject line helps to quickly convey the purpose of the message and be easily found in the inbox. Call it what it is: 

  • Reset your password at AppName
  • AppName weekly report
  • Confirmed! Proceed with your AppName account
  • AppName payment failed. Your action is required

We have listed several good subject line examples above. As a rule of thumb, don’t use exclamation marks and don’t emphasize words by typing with all capital letters. This is bad etiquette, and spam filters don’t like it either.

Inspect Your Emails

Email template

There are many rules about email templates, that’s for sure. Here is a helpful list of some things that affect deliverability and performance in general. 

  1. Don’t abuse images, gifs, explainer videos, or other media elements.
  2. Try to keep the overall emails size up to 100 KB.
  3. Wherever possible, don’t attach files – it is better to make them available for downloading via a link.
  4. Keep email template width up to 680 pixels.
  5. Include unsubscribe option, for all types of transactional emails, to comply with CAN-SPAM, GDPR, and other regulations. 

There are many ways for building email templates

  • Code an HTML template manually (recommended for experienced developers – web and email development are two big differences)
  • Pick one of the email frameworks, such as MJML or HEML
  • Try a set of HTML patterns or ready to use email templates, such as Cerberus
  • Choose from a list of email builders, which allow editing and exporting HTML code (Email Monster, BEE Free, etc.)

Further reading

Email testing

Notwithstanding the method you choose for building transactional messages, you need to set an efficient email testing workflow. 

Here is what you need to test:

  1. Email sending script. Make sure that user actions trigger proper email sending scenarios. (For example, when a user presses “reset password button, they receive an email with a link for setting a new password).
  2. Email sending capacities, or load testing. You should be able to handle high loads, when a significant number of users simultaneously performs an action that triggers email sending. 
  3. Email deliverability. At the very least, check your spam score and domain blacklisting.
  4. Email content. In transactional emails, dynamic content and personalization play a significant role. Make sure they work properly by testing all messages, not just one from the whole batch.
    Preview your emails and analyze possible HTML/CSS errors – there are no email rendering standards across email clients. Your users should be able to view and understand your message on any device, type of email client, or browser. 

Run all tests in a pre-production environment and isolate your staging from production. 

Start Testing

Further reading


We have shared the most essential tips for building effective transactional emails, focusing on the aspects that are commonly overlooked by developers. For some inspiration and good examples of different types of messages, click the articles below and make sure that you are fully equipped to send transactional emails that your users will love. 

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