System Variables

Posta reserves the {{ posta_* }} variable namespace for values it injects into every templated email. You don't pass these in template_data — Posta fills them in per message, after the message identity is known. Using them is opt-in: a variable only appears if your template references it.

The posta_ prefix is reserved. Any key you supply in template_data that starts with posta_ is ignored in favour of the system value.

Available variables

Variable	Description
{{ posta_web_view_url }}	Signed link to read this email on the web ("view in browser").
{{ posta_mail_web_link }}	Alias for posta_web_view_url.
{{ posta_unsubscribe_url }}	One-click unsubscribe link for this message.

View in browser

<a href="{{ posta_web_view_url }}">View this email in your browser</a>

Works in the text part too:

View online: {{ posta_web_view_url }}

The link is an HMAC-signed, expiring capability bound to the message's opaque ID. The hosted page renders the exact HTML that was sent, on Posta's public web origin (POSTA_WEB_URL), with a restrictive content-security policy, noindex, and no cookies. Opening it does not count as an email open.

Notes:

• Links expire after 90 days by default.
• cid: inline-attachment images don't resolve on the web — use https/data: image URLs if you rely on the web view.

Unsubscribe

<a href="{{ posta_unsubscribe_url }}">Unsubscribe</a>

For campaign sends this unsubscribes the recipient from that campaign's list. For transactional sends it adds the recipient to your suppression list. The link is the RFC 8058 one-click endpoint, so it also works from the mailbox-provider "Unsubscribe" button.

Behaviour in previews

In the template editor / preview there is no real message yet, so each system variable renders as its own name (e.g. {{ posta_web_view_url }} → posta_web_view_url) rather than a generated link. This lets a preview of a template that uses system variables render without errors, and shows the author which variable sits where. The real links are only generated when the message is actually sent.