Comparison

Sovereign Mail vs Postmark

An honest comparison. Both send transactional email well; the real difference is UK sovereignty and privacy versus Postmark's proven deliverability track record and maturity.

Choose Sovereign Mail if…

you need UK data sovereignty (NHS, government, regulated business), want no recipient tracking, prefer UK bank transfer/invoicing, or want a lower price.

Choose Postmark if…

you need a long, proven deliverability track record today, inbound email parsing, or the most mature analytics — and US data jurisdiction isn't a concern for you.

Switching from Postmark is quick

The APIs are close cousins, so for most apps the code change takes under an hour. Your DNS can serve both providers at once, so there's no cut-over day: move traffic across when you're ready.

1. Create an account and add your sending domain. Publish the DNS records we show you. They sit alongside Postmark's (each provider signs with its own DKIM key), so both keep working during the switch. If your domain already has an SPF record, add our include: to it rather than creating a second one.
2. Swap the API call. Same shape, different names:

   Postmark	Sovereign Mail
   POST https://api.postmarkapp.com/email	POST /api/v1/email
   X-Postmark-Server-Token: …	Authorization: Bearer smk_live_…
   From	from — a bare address (no "Name <…>" yet)
   To — up to 50, comma-separated	to — one address; use batch for several
   Subject · TextBody · HtmlBody	subject · text · html
   /email/withTemplate — TemplateId + TemplateModel	/email — templateId + variables (string values)
   /email/batch — an array, up to 500	/email/batch — { "messages": [ … ] }, up to 500
   MessageStream	Not needed — transactional only
   TrackOpens · TrackLinks	Not available — we never track recipients
   Bounce & spam-complaint webhooks	Applied automatically: the address is suppressed

   Before · Postmark

   curl https://api.postmarkapp.com/email \
     -H "X-Postmark-Server-Token: $POSTMARK_TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"From":"noreply@example.co.uk","To":"user@example.org",
          "Subject":"Reset your password","TextBody":"…","MessageStream":"outbound"}'

   After · Sovereign Mail

   curl https://sovmail.co.uk/api/v1/email \
     -H "Authorization: Bearer $SOVMAIL_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{"from":"noreply@example.co.uk","to":"user@example.org",
          "subject":"Reset your password","text":"…"}'

3. Test without sending anything. Use a test key (smk_test_…): every request is checked and recorded exactly as live, but nothing is delivered and nothing counts against your plan.
4. Switch over. Put the new path behind a config switch, send a share of your traffic, then all of it. Keep Postmark for a week as a fallback.

Or let your AI assistant do it

Paste this into Claude, ChatGPT, Gemini, Copilot or Cursor in your project. It points the assistant at our machine-readable guide, so it uses the real API instead of guessing.

What works differently

• Postmark templates use {{name}} placeholders, like ours. Mustachio sections ({{#name}}…{{/name}}) become {{#if name}}…{{/if}}, and {{#each}} loops aren't supported yet.
• Your Postmark suppressions live per message stream. Export them from each stream you send on.
• One recipient per message. Where you sent to several addresses at once, send one message each, or use batch (up to 500 per call).
• No display name in the from-address yet: noreply@example.co.uk, not "Example <noreply@…>".
• No cc, bcc, reply-to, custom headers or attachments yet. Unknown fields are ignored, not rejected, so check your code doesn't rely on them.
• REST API only: no SMTP relay yet.
• Template variables are strings. Format numbers and dates before you send them.
• Bounces and spam complaints aren't sent to you as webhooks. We suppress the address automatically, so you don't need to act on them.
• Your old provider's suppression list doesn't carry over automatically. Export it and add the addresses on the Suppressions page (there's no bulk import yet).
• Our sending IPs are newer, so start by moving part of your traffic. Limits rise as your sending history builds.

Moving from somewhere else? Switching guides for Mailgun, MailerSend, Mailjet, SMTP2GO, SendGrid, Amazon SES and Resend.

Frequently asked questions