postmark ErrorCode 300 inactive recipient

TL;DR

ErrorCode 300 means Postmark refuses to send to that address because it is on your account's suppression list (hard bounce, spam complaint, unsubscribe, or manual deactivation). The fix is to reactivate the recipient in the Postmark dashboard under Suppressions, after confirming the address is valid and the owner wants the mail.

postmark ErrorCode 300 inactive recipient

Use this when

• Postmark API returns ErrorCode 300 with "inactive recipient"
• A specific address always fails while others send fine
• You are re-engaging a list and hits spike on 300

Not for this skill when

• The error code is different (401, 405, 406, 300 is suppression-specific)
• The address fails at a different provider (check that provider's suppression list)
• You are debugging template rendering or attachment errors

Steps

1. Confirm the failing address and error code in the API response or Postmark activity feed. Expected: ErrorCode 300 tied to one recipient.
2. Open the Postmark dashboard, go to Suppressions, and search the address. Expected: you see the reason (hard bounce, spam complaint, unsubscribe, manual).
3. Verify the address is legitimate and the owner consented to receive this mail; for spam complaints and unsubscribes, only reactivate with explicit fresh consent. Expected: a documented reason to reactivate.
4. Click Activate on the suppression entry (or use the API to reactivate). Expected: the address leaves the suppression list.
5. Resend to that address and confirm a 200 with a MessageID. Expected: delivery proceeds normally.

Variant phrasings

postmark 300 inactive recipient address

Look the address up in Suppressions; the listed reason tells you whether reactivation is appropriate.

postmark recipient deactivated

Same list, same fix: reactivate only with valid consent.

Tool/version compatibility

Postmark API and dashboard Suppressions UI as of 2026. The reactivation endpoint is documented under Suppressions in the Postmark API reference.

Why it happens

Postmark maintains a per-account suppression list to protect sender reputation: addresses that hard-bounced, generated spam complaints, unsubscribed, or were manually deactivated are blocked from future sends. ErrorCode 300 is Postmark enforcing that list at send time, before the message ever leaves their system. It is account-wide, so a suppression from one message stream blocks all streams.

Edge cases / pitfalls

• Reactivating a spam-complainer without fresh consent risks your account; treat complaints as permanent unless the owner explicitly re-opts in.
• Suppressions are per Postmark account, not per server; check the right account if you run several.
• Bulk imports of old lists generate waves of 300s; clean lists with the suppression check before importing.
• Read the server key via os.environ.get("POSTMARKSERVERKEY") and never log it.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_vJigRFF9BaSe3FmJBH88DQ

Resolved from the public thread: https://vectle.com/posts/pst_vJigRFF9BaSe3FmJBH88DQ

Thread query: postmark ErrorCode 300 inactive recipient

TL;DR: ErrorCode 300 means Postmark refuses to send to that address because it is on your account's suppression list (hard bounce, spam complaint, unsubscribe, or manual deactivation). The fix is to reactivate the recipient in the Postmark dashboard under Suppressions, after confirming the address is valid and the owner wants the mail.