When a sending domain has been added to a third-party external blocklist and email deliverability has declined, follow the steps below to assess the situation, implement root-cause fixes, and gradually resume sending after delisting.

Assess the Situation

Blocklist criteria used by external organizations are not publicly disclosed and are generally difficult to identify from the sender's side. Focus on understanding the current state and determining the appropriate response. From an MCE perspective, use the following methods to assess the situation. None of these checks are mandatory — using any one of them to understand the current state is sufficient.

Review MCE Reports and Data Views

• In Email Studio Reports (or Analytics Builder > Reports), review the "Spam Complaints Over Time" report. 
• Use the _Bounce data view extracted via Automation Studio to check bounce reasons: 
  
  • Confirm that BounceCategory shows "Block bounce."
  • Check the bounce message (SMTPBounceReason) for references to a specific blocklist name or phrases such as "Blocked due to spam or sender reputation issue."

Consider Using External Tools

MCE data alone may not be sufficient to understand ISP-side filtering behavior. If needed, use external reputation-checking tools to verify IP address and domain reputation, and assess whether your sending domain is being flagged or listed.

Address the Root Cause

Before resuming delivery, verify sender domain authentication and evaluate the quality of your sending list and email content. Identifying and resolving potential blocklist triggers reduces the risk of being relisted.

Verify Sender Domain Authentication

Confirm that the domain used in the From address is configured as a SAP (Sender Authentication Package) or Private Domain. Sending from an unauthenticated domain (e.g., Registered Domain or Verified Individual From Address) causes SPF / DKIM / DMARC authentication failures and is a direct cause of blocking.

Optimize the Sending List

• Validate addresses and avoid sending spikes: To prevent hard bounces from invalid addresses, consider sending only after confirming validity through double opt-in, or avoid bulk sends to new users all at once.
• Address low-engagement subscribers: Consider removing readers who have shown no engagement (opens, clicks, etc.) over a defined period, based on your sending frequency.
• Target active subscribers only: Restrict delivery to confirmed opt-in users to prevent spam trap hits and complaint submissions.

Review Email Content

• Link validity: Check for broken links (404 errors) or redirects to low-reputation external domains in the email body.
• Targeting and frequency: Verify that you are not sending at excessive frequency or with sudden volume spikes to specific segments, and that the content is relevant to the target audience. Adjust as needed.
• Text and language: Check subject lines and body text for overly aggressive language or spam-trigger words. Correct any that are found.
• Isolate tracking URLs: Temporarily disable click tracking in your send settings and perform a test send to determine whether a specific tracking URL is contributing to the block.

Resume Delivery and Monitor Performance

After implementing improvements, submit a delisting request, then gradually increase send volume while monitoring bounce and complaint rates.

Submit a Delisting Request

The delisting procedure differs depending on your IP environment (dedicated or shared):

• Dedicated IP: Because a dedicated IP's reputation depends solely on your own sending history, visit the blocklist operator's website and submit a delisting request directly.
• Shared IP: Because customers on shared IPs may be unable to submit delisting requests directly, open a case with Salesforce Support as soon as possible.

Control Volume and Monitor After Resuming

1. After the delisting request is accepted, do not send in bulk immediately. Resume delivery gradually by controlling volume — use the same approach as IP warming. 
2. To prevent relisting and severe penalties from resuming before the root cause is resolved, check bounce rates and complaint rates after every send once delivery resumes. If you see signs of deterioration, stop sending immediately.