Form Notification Not Sending to One Internal Email (Previously Working)

Marketing & Content Hub Email Deliverability
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1

Hi Community,

We’ve been using HubSpot Free to collect leads through our form and send internal notifications to multiple team emails.

Since May 20, one recipient has stopped receiving notifications even though:

  • They were receiving them before without issue
  • The email is still listed in the “Send submission notifications to” field
  • Other recipients are receiving as usual
  • We’ve checked spam, junk, and re-added the address

We suspect this email might have bounced or been suppressed/unsubscribed, but we can’t confirm it under the Free Plan.

Could someone from the HubSpot Team or Community help us check if this email is on a suppression list?

Thanks,
Lynnette @ PriooCare

2

Hello @Prioocare ,

I’ve encountered a similar issue with one of my accounts. After reaching out to the HubSpot team, they informed me that internal form notification emails can sometimes fail to deliver due to a soft bounce error, specifically 'THROTTLING_BOUNCE'. This typically occurs when the recipient’s email server enforces a rate limit on the number of incoming emails per minute from HubSpot’s notification address (noreply@notifications.hubspot.com).

In your situation, it’s likely that the affected internal email address hit this threshold, even though others are still receiving the notifications. This can result in temporary delivery failures or suppression for that specific address.

To fix this, HubSpot recommends working with your IT team to:

  • Allowlist these HubSpot IP ranges on your email server:

    • 108.179.150.0/23
    • 108.179.152.0/24
    • 108.179.153.0/26
    • 108.179.153.64/27
    • 108.179.153.96/28
    • 108.179.153.112/30

  • Check if your email security provider (like Proofpoint) is applying throttling or deferring messages with a 421 Deferred error.

If you’re using a provider like Proofpoint, it’s best to reach out to them directly to understand why these emails might be getting throttled. If any support case numbers are generated, sharing them with HubSpot can help speed up the investigation.

Hope this helps clear things up!