Why are brand new contacts being marked as hard bounce?

ola

Hi everyone,

I uploaded an external list into my Marketo instance (one that we've never used before) and found that many of the contacts on said list had emailing suspended due to "hard bounce." How is this possible when they're brand new and I've not yet sent them a single email?

SanfordWhiteman

Please show the (unfiltered) Activity Log for one such lead.

Kristof

⚠️ This post has been edited by a moderator for accuracy.
It’s our responsibility as a community to not provide AI-hallucinated and/or untested answers.

Hey @ola

I've seen this happen before, and there may be a few possible reasons why brand-new contacts are being marked as hard bounces right after upload:

1. Marketo's global blacklist (Durable Bounce & Email Suspended history)

Marketo keeps a global record of hard bounces. If an email address bounced hard in the past, even in a different Marketo instance, the system automatically flags it as email invalid or email suspended the moment it gets added again—even if it’s brand new to your database.

2. 'Email Suspended' status sticking around

If an email was already in your instance at some point and previously bounced, re-uploading it won’t reset its status. Marketo won’t “reactivate” an email once it’s been marked as suspended. Check the Email Suspended Cause field—it might give you a clue as to what happened.

3. List quality issues

If the list is purchased, scraped, or just not super fresh, some emails might be spam traps, inactive, or invalid addresses that already bounced elsewhere. Marketo catches that and flags them right away.

4. Marketo’s email deliverability checks

Depending on your setup, Marketo might be using an email validation service (like BrightVerify, Kickbox, etc.). If that service has already identified the email as invalid, Marketo won’t even attempt to send to it—it’ll just label it as a hard bounce from the start. Just an optional cause in general in case you use external services.

5. ISP-Level Blocking - before you Even send anything

Some email providers (especially Gmail, Yahoo, corporate domains) have internal blocklists. If the email address was previously flagged as non-existent or spammy, Marketo won’t send to it—and it'll get marked as a hard bounce immediately.

What You Can Do:

Check the system fields in Marketo:
- Email Invalid
- Email Suspended
- Email Suspended Cause
- Durable Bounce Reason
Validate the list externally
- Export the bounced emails and run them through an email validation tool (like NeverBounce, ZeroBounce, etc.).
Test sending to a small batch
- Try a test send to a handful of these contacts. If all of them bounce, that’s a red flag for the whole list.
If you’re sure the emails are legit, you can try reaching out to Marketo Support—they might be able to clear some of the email suspended statuses manually.

Hope this helps!

SanfordWhiteman

Some of the claims in this reply sound like hallucinations. What Marketo subscription automatically calls the BriteVerify or Kickbox API without user intervention?

The best approach is to look at the Activity Log. Marketo is quite good at explaining each change made to new leads, including those made by automatic system campaigns.

SanfordWhiteman

2. 'Email Suspended' status sticking around

If an email was already in your instance at some point and previously bounced, re-uploading it won’t reset its status. Marketo won’t “reactivate” an email once it’s been marked as suspended. Check the Email Suspended Cause field—it might give you a clue as to what happened.

This is not true, easily disproven with a simple test.

Did you actually observe this happening? If so, do you have logs & screenshots tracing all the steps?

Why are brand new contacts being marked as hard bounce?