Email Blocking for Invalid or Restricted Recipient Domains

Modified on: Wed, 13 May, 2026 at 9:55 PM

Email Security

Restricted Domain Blocking for Outbound Emails

A pre-send validation that blocks emails to invalid or restricted recipient domains — protecting your deliverability and reducing security risk.

What You'll Learn

The platform blocks outbound emails before sending when the recipient email domain is invalid or restricted for security reasons. This prevents sends to domains that can increase security risk or lead to failed delivery — keeping your sender reputation safe.

Table of Contents

What Is Restricted Domain Blocking?

Frequently Asked Questions

What Is Restricted Domain Blocking?

Restricted Domain Blocking is a pre-send validation that prevents outbound email when a contact's email domain (the part after @) is invalid or restricted. When the block triggers, the platform does not attempt to send the email.

Key Benefits

Reduces failed sends — stops emails that would likely fail delivery anyway.

Protects deliverability — fewer hard bounces means less risk to your sender reputation.

Improves security — prevents sending to domains restricted for security reasons.

How It Works

Step 1

Validate the recipient domain

The platform validates the recipient email address domain before attempting to send.

Step 2

Block if invalid or restricted

If the domain is invalid or restricted, the platform blocks the send before it leaves.

Step 3

Email is unusable until updated

The contact's email cannot be used for outbound communications until the address is updated to one on a permitted domain.

Restricted Domain Blocking validation flow

What You Will See

When an email address is blocked, an inline warning appears under the contact's Email field:

Warning Message

"This email address is invalid as the domain is restricted for security reasons."

Inline warning under the contact's Email field showing the restricted-domain block message

How to Resolve

Step 1

Confirm the email address is correct

Check for typos — especially in the domain after the @ symbol.

Step 2

Update the contact with a valid email

Replace the address with a valid email on a permitted domain. Once updated, outbound sends can resume normally.

Step 3

Contact Support if the recipient is business-critical

If this is a recipient domain you genuinely need to reach, raise a Support ticket and include:

The recipient domain (example: example.com)
Where you saw the warning (Contact record, Conversations, Campaigns, Workflows, etc.)
The sub-account name or ID
The sending method (LC Email, Mailgun, or custom SMTP)

Note

There is no in-app override for the block. The address must be replaced with a permitted one for sending to resume.

Frequently Asked Questions

Q: Can I still send to an email address that shows this warning?

No. The platform blocks the send before it leaves the system when the recipient domain is invalid or restricted.

Q: Can I override or bypass the block?

No. You must update the contact with a valid email address on a permitted domain.

Q: Where do I see the warning?

An inline warning appears under the contact's Email field whenever a blocked address is loaded or entered.

Q: Does the platform attempt delivery anyway?

No. When this warning appears, no send is attempted — campaigns, workflows, and manual sends to that address are all blocked at the validation step.

Q: How do I prevent this from happening?

Verify recipient email addresses at intake — use form validation, double opt-in, and an email verification service — and proactively correct typos in the domain after @ before attempting to send.

Q: Does this apply to all sending methods?

Yes. The pre-send validation runs regardless of whether you're using LC Email, Mailgun, or a custom SMTP integration.

Q: Do blocked sends count against my bounce rate?

No. Because nothing is ever sent, blocked addresses don't generate a bounce — that's actually one of the protections this feature provides for your sender reputation.