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Introduction

This error occurs when attempting to send email from a domain that is not authorized for your SMTP user account.

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Example Error Message

Here’s what this error looks like: 
user@example.com
   host relay.jetsmtp.net [103.173.0.0]
   SMTP error from remote mail server after end of data:
   550 [ACL] Blocked. See https://reports.jetsmtp.net/?id=000000000000000000&auth=smtpuser

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What Does This Mean?

Our access control system has blocked your email because:
  • The sending domain is not authorized for your account
  • Your SMTP credentials don’t have permission to send from this domain
  • Domain authentication hasn’t been properly configured

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How to Fix This Error

Check the SMTP user’s permission mode first. The most common cause of this block is the SMTP user not being allowed to send from the From domain. Open Outbound → SMTP → your SMTP user and check the permission mode:
  • Default: only domains explicitly assigned to this user. Add the sender domain to the user’s allowed list.
  • Allow all domains: any domain on your account. If your sender domain isn’t in Outbound → Domains yet, add it there.
  • Allow any domain (Pro): any domain at all. If you’re on Pro and expect this, make sure the toggle is actually on.
See SMTP users → permission modes for the full breakdown.
  1. Verify the “From” address matches a domain the SMTP user is allowed to send from (see note above)
  2. Check the SMTP user’s permission mode and adjust if needed
  3. If the domain should exist on your account, add and verify it under Outbound → Domains
  4. Ensure proper SPF and DKIM records are configured for the sending domain

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Prevention

To avoid this error in the future:
  • Only send from domains that are authorized for your account
  • Keep an updated list of your approved sending domains
  • Request domain authorization before attempting to send
  • Regularly review your account’s domain settings