Constant Contact email API: SDKs, docs and limits (2026)

From Constant Contact's official docs · checked 10 September 2026

Docs, SDKs and limits

Developer docs

v3.developer.constantcontact.com/api_guide/index.html

API reference

v3.developer.constantcontact.com/api_reference/index.html

Rate limits

Up to 10,000 requests per day and 4 requests per second; the daily count resets at 00:00 UTC. Source

From our feature matrix — documented by the vendor

API, SMTP and sending auth

• ✓APIV3 REST API ('99.99% uptime'); higher rate limits via Tech Partner Program; plan gating still unstated on portal
• ✓SDKs / client librariesOpen-source V3 SDKs on GitHub: C# (.NET), PHP, Python, Ruby, TypeScript
• ✓Public API docsPublic developer portal exists (v3 API); plan gating unstated
• ◐WebhooksWebhooks exist but as 'Partner Webhooks' for technology partners only (subscription topics e.g. cancelled accounts); no general customer event webhooks documented
• —SMTP APINot documented — browser pass 2026-08-21: no SMTP/send API on the v3 developer portal
• —SMTP relayNot documented — browser pass 2026-08-21: no SMTP relay offering on site or developer portal
• —Transactional emailNot documented — browser pass 2026-08-21: no transactional email product anywhere on constantcontact.com features nav or the v3 developer portal (API is campaign-based)
• ◐SPF assistanceKB guidance on SPF ('Should I add Constant Contact IP addresses to my SPF record?'); auth is DKIM-CNAME based
• ✓DKIM setupSelf-authentication with DKIM CNAME (or TXT) records generated by Constant Contact
• ✓DMARC supportConstant Contact generates the DMARC record names/values to add to DNS

Features checked 10 September 2026. ✓ documented · ◐ limited or plan-gated · × documented as absent · — not documented. Documentation is not a measured result — see our methodology.

Pricing snapshot

Generated from our datasets — every value verified and dated

Frequently asked questions