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Email Foundations



This Onboarding Guide is recommended for a direct brand. A direct brand sends email to its own customers directly. Alternatively, an independent software vendor (ISV) uses Twilio SendGrid to send email on behalf of its customers. The architecture described is not ideal for an ISV. See an example ISV architecture on the Twilio SendGrid blog(link takes you to an external page).

Welcome to "Email Foundations," the first milestone in the Twilio SendGrid Web API Onboarding Guide. This milestone is designed for anyone that would like to understand the fundamentals of how email works.

By the end of this milestone, you'll be able to:

  • Recognize the most important concepts pertaining to how email works
  • Understand your options for sending email through Twilio SendGrid
  • Understand the steps in the process of building your email application

Factors that affect the deliverability of email

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It helps to understand a few concepts that will come up as your team builds your email application. These building blocks of the email ecosystem matter because they interact to facilitate — or prevent — the delivery of your content to your target inboxes.


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DNS stands for Domain Name System, and it's thought of as the phone book for the Internet. This is because DNS records tell us where to find resources on the internet by resolving domain names to IP addresses. IP addresses are assigned to machines where resources can be delivered or retrieved. DNS records house many pieces of information for the sending domain of a message. The receiving server checks this "phone book" to see if it can determine who the sender is and if they are trusted.

Email authentication is a set of protocols that internet service providers (ISPs) use to verify the trustworthiness of the email you send. Based on these protocols, the recipient's mailbox provider will determine whether to deliver your message directly to the inbox, to the spam folder, or not at all.

Specifically, the receiving server will check:

Twilio SendGrid's sender authentication feature assists with setting up both SPF and DKIM properly. These settings ensure the recipient's mailbox provider recognizes the host (or sender) and that the content is trustworthy.

Every time you send email, ISPs collect data that tells them about your sending practices. As a result, both your domain (what appears after the @ symbol in your email address) and your IPs (which are unique sending identifiers) will develop a reputation.

To determine your IP and domain reputation, the receiving server will factor in:

  • The reaction of its other recipients to mail sent by that same IP and domain, such as whether it was marked as spam or not.
  • Where the receiving server previously decided to place any mail from the same IP and domain.

A good reputation is something that you can cultivate through solid program infrastructure, a methodical IP warm-up, list hygiene (sending to people who want your email), and good content, to name a few. We'll cover each of these strategies in the milestones of this onboarding guide.

  • Learn how email works.
  • Review your sending options (Web API, SMTP, or Marketing Campaigns).
  • Understand the onboarding process.

Evaluate and Plan Your Strategy

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  • Align your team around your development strategy.
  • Develop your target email account architecture.

Build and Test Your Application

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  • Set up your account.
  • Manage Subusers.
  • Complete authentication.
  • Configure settings.
  • Integrate and test your mail send.
  • Warm up your IP(s).
  • Monitor your email program.
  • Hone your content strategy.
  • Optimize your deliverability.

Many of these steps can be completed by non-technical team members, but there are technical actions along the way. We'll recommend when you should have a technical resource on hand.

Next, Evaluate and Plan Your Strategy

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