supermarket

Send email

Postmark

Email delivery service with REST API, SMTP, webhooks and inbound parsing for transactional and broadcast email.

Rate limits

Numeric request limit
Not published
Over-limit response
HTTP 429 when requests exceed acceptable use of the API5
Daily sending limit
Unlimited emails a day on paid plans1

Other limits

Message size
10 MB including attachments3
Body size
5 MB each for text and HTML bodies3
Recipients per message
50 across To, Cc and Bcc6
Batch size
500 messages and 50 MB per /email/batch call6
Bulk API payload
50 MB including attachments7
Spam complaint rate
Must stay under 0.1% of emails20
Bounce rate
Must stay under 10% of emails20
Webhook retries
Up to 6 retries, 1 to 15 minutes apart, for 5xx, 408, 429 and network failures8

Read from ActiveCampaign’s own pages on 2026-11-04. Every number links to the page a value came from. For agents, the same facts as markdown: /tools/send-email/postmark.md