Postmark
./CommunicateTransactional email with high deliverability and detailed delivery webhooks
OpenAPIllms.txt
$ protocol support
$ payment protocols
none documented — this service is not reachable over an agent payment protocol
$ agent access
authAPI Key
onboardingPartial — dashboard signup, then API key
tosNeutral — no bot restrictions
webhooksYes
free tierNo
billingpay-per-request
#email#transactional#deliverability
https://postmarkapp.com
// last verified 8/26/2026
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