How to Send Emails from Shopify Flow Using Postmark

Go to account.postmarkapp.com/sign_up and register with your name, work email, and a password.

Every new account starts on the free Developer plan, which sends up to 100 emails a month with no card required and no expiration. That’s enough to get FlowRelay connected and tested. When you’re ready for real volume, paid plans start with Basic at $15/mo for 10,000 emails, with Pro and Platform tiers above that. Check postmarkapp.com/pricing for current numbers.

In the Postmark dashboard, open Sender Signatures and add the domain you want to send from (a subdomain such as mail.yourstore.com works well).

Verifying a domain, rather than a single address, is what enables DKIM signing and a custom Return-Path for your domain, which a plain Sender Signature doesn’t cover. Postmark gives you DNS records to add through your domain registrar or DNS host: a DKIM TXT record and a Return-Path CNAME record. Once they’re saved, Postmark checks them automatically; verification can take up to 48 hours to clear.

Postmark organizes sending through Servers, and each one carries its own API token. From your dashboard, create a Server for your store (or use the default one your account starts with).

Open that Server, go to API Tokens, and copy the Server API Token shown there. This is the token FlowRelay needs, not the account-level API token used for managing servers. Keep it somewhere safe; you can regenerate it from the same page if it ever leaks.

Install FlowRelay from the Shopify App Store and accept the requested permissions.

On first launch, FlowRelay shows a short setup checklist: set your sender name and email, connect a provider, and send a test email. The next two steps cover connecting Postmark.

In FlowRelay, open Settings, find Email delivery, and click Manage providers to open the Connect email provider dialog.

Pick Postmark from the provider list and paste in the Server API Token you copied. FlowRelay checks that the token is valid before saving it. If you want emails to go out under a different name or address than your account default, open Override sender and fill those in, and turn on open or click tracking if you’d like Postmark to report on those events.

Click Connect. Whichever provider you connect first becomes your Primary, and FlowRelay routes all outbound mail through it. You can connect a second provider later as an automatic Fallback.

Open Shopify Flow, create a new workflow, and pick a trigger (Order created is a common one to start with). Add the Send transactional email action; it shows up in the action list once FlowRelay is installed.

You’ll need to fill in a few fields on the action: an email address for the recipient (this can pull straight from the trigger, like the customer’s email), a subject line, and the body, which is the actual HTML content of the email. There’s also an optional preview text field for the snippet shown in inbox previews. For the body, you can write plain HTML or use Liquid to pull in order details, customer names, and other data from the workflow.

Save the workflow and turn it on.

Before you trust a live trigger, use the Send test email button in FlowRelay’s settings. It confirms Postmark is wired up correctly and shows you where the message lands.

Once that test email arrives, run your Flow workflow under real conditions, like placing a test order, and check FlowRelay’s delivery log to confirm the email went out through Postmark and see its delivery status.