Is Senlo a Postmark alternative?

No. Postmark keeps delivering your email: Senlo renders the template and sends the finished message through Postmark's API with your server token. Your sender signatures, reputation and Postmark bill stay where they are.

Do I keep using Postmark's templates?

No. The template lives in Senlo, and your code calls POST /api/triggered instead of /email/withTemplate. Postmark receives ready HTML and text. Old Postmark templates can stay until everything has moved.

Do bounces and complaints still work?

Yes. Add a webhook in Postmark pointing at Senlo, and deliveries, bounces, spam complaints, opens and clicks show up in Senlo's dashboard; a hard bounce suppresses the address before the next send.

Which message stream does Senlo use?

Your server's default transactional stream. Picking a broadcast stream is not there yet, so keep sequences to emails Postmark counts as transactional, such as a welcome series after sign-up, and send marketing elsewhere.

Can I import my Postmark templates?

Not yet. Rebuild them in the editor, using the Postmark HTML as a reference; Mustachio's {{#each}} becomes a table bound to your data and its sections become conditions.

What does it cost on top of Postmark?

Senlo Cloud is free for one person up to 3,000 emails a month $19 a month for up to 50,000 with a team, and $59 for up to 250,000. Self-hosted, it costs a small server.

Use case · Postmark

A visual template editor on top of Postmark.

Postmark is excellent at delivering email; its templates are code. Senlo adds the editor your whole team can use, real if/else conditions and onboarding sequences, and sends every message through your Postmark server as before. Postmark keeps the delivery, the logs and the bounces.

Edit without the HTML

Rows, columns, merge tags and conditions in a drag-and-drop editor, previewed with real data. Developers get the same template through the API.

No push step

Save in the browser and the next send uses it. No Git repository and push step just to fix a typo, no 100-template ceiling per server.

Postmark still sends

Senlo uses Postmark's API with your server token and reads its webhooks, so deliveries, bounces and complaints land in Senlo's dashboard too.

Before and after

A receipt with order lines, the Postmark way and the Senlo way.

Postmark: Mustachio in the template, a model in the call

<!-- receipt template, one part of ~560 lines of HTML -->
{{#each receipt_details}}
<tr>
  <td class="purchase_item">{{description}}</td>
  <td class="align-right">{{amount}}</td>
</tr>
{{/each}}

curl https://api.postmarkapp.com/email/withTemplate \
  -H "X-Postmark-Server-Token: ..." \
  -d '{ "TemplateAlias": "receipt", "To": "ana@example.com",
        "TemplateModel": { "receipt_details": [...], "total": "$15.00" } }'

Senlo: the template is built in the editor

# same order lines, a table block bound to the data; Postmark delivers
curl -X POST https://senlo.io/api/triggered \
  -H "Authorization: Bearer snl_..." \
  -H "Content-Type: application/json" \
  -d '{
    "id": "receipt",
    "to": "ana@example.com",
    "data": { "receipt_details": [...], "total": "$15.00" }
  }'

Postmark templates and Senlo, feature by feature

Feature	Senlo	Postmark templates
Drag-and-drop editor Postmark templates are HTML and text code with a live preview; visual tools such as Stripo export into them.
Editable by people who don't write code
If/else conditions on values Mustachio shows a section when a value is present; it has no if/else and no formatting helpers.
Lists from your data (order lines)
Shared layout and reusable parts Postmark Layouts; Senlo saved rows.
Version history and rollback Postmark documents none and suggests Git with postmark-cli. Senlo has undo and redo while you edit; saved versions are on the roadmap.
More than 100 templates Postmark allows up to 100 templates per server.
Sequences: event triggers, waits and branches
Templates keep working if you change provider

From Postmark's templates API and templates FAQ, checked 2026-11-02.

Connect Postmark in four steps

1
Copy a server token
In Postmark, open the server you send from and copy its Server API token from API Tokens.
2
Add Postmark in Senlo
On the Providers page, paste the token and a webhook secret of your choosing, then send a test email.
3
Add the webhook
In Postmark's Webhooks, point at https://senlo.io/api/webhooks/postmark with a custom header X-Postmark-Secret set to that secret.
4
Build and send
Create the template in the editor, then call POST /api/triggered with its id, the recipient and the data.

What to know before you start

Works today

Sending through Postmark's API with your server token.
Deliveries, bounces, spam complaints, opens and clicks from Postmark's webhooks.
Suppression after a hard bounce, before the next send.
List-Unsubscribe headers and an unsubscribe page.

Not yet

Choosing a message stream: everything goes to the server's default transactional stream.
Importing Postmark templates: rebuild them in the editor.

What it adds to your bill

Your Postmark bill does not change: Postmark keeps delivering at its own rate. Senlo is the only addition, and it is priced by emails sent, not by contacts.

Free

$0 / month

Up to 3,000 emails and 1,000 automation runs a month, one person.

Pro

$19 / month

Up to 50,000 emails and 10,000 automation runs a month, 5 people with roles and a 30-day audit log.

Team

$59 / month

Up to 250,000 emails and 100,000 automation runs a month, unlimited people with roles and a 90-day audit log.

Self-hosted

≈ $8 / month

The same code, AGPL-3.0, on a 4 GB VPS of your own, any volume. Plus your time on upgrades and backups.

Above 250,000 emails a month Senlo Cloud has no plan: self-host, or write to us. Details on the pricing page.

Developers on managing Postmark templates

Including Postmark's own words. Linked to the source.

“The workflow to make changes to templates, and then move them from one server to the next, is time-consuming and error-prone.”

Postmark's own blog, 2018

“email:push was a manual step no workflow ran, so a template PR could go green, merge, and change nothing members receive.”

A pull request on GitHub, 2026

“we really value an ability to edit html/text for a non-developers which saves a lot of time”

postmark-rails issue on GitHub, 2018

Questions

Is Senlo a Postmark alternative?: No. Postmark keeps delivering your email: Senlo renders the template and sends the finished message through Postmark's API with your server token. Your sender signatures, reputation and Postmark bill stay where they are.
Do I keep using Postmark's templates?: No. The template lives in Senlo, and your code calls POST /api/triggered instead of /email/withTemplate. Postmark receives ready HTML and text. Old Postmark templates can stay until everything has moved.
Do bounces and complaints still work?: Yes. Add a webhook in Postmark pointing at Senlo, and deliveries, bounces, spam complaints, opens and clicks show up in Senlo's dashboard; a hard bounce suppresses the address before the next send.
Which message stream does Senlo use?: Your server's default transactional stream. Picking a broadcast stream is not there yet, so keep sequences to emails Postmark counts as transactional, such as a welcome series after sign-up, and send marketing elsewhere.
Can I import my Postmark templates?: Not yet. Rebuild them in the editor, using the Postmark HTML as a reference; Mustachio's {{#each}} becomes a table bound to your data and its sections become conditions.
What does it cost on top of Postmark?: Senlo Cloud is free for one person up to 3,000 emails a month $19 a month for up to 50,000 with a team, and $59 for up to 250,000. Self-hosted, it costs a small server.