Unusual bounce increase

If you’re using a standard shared Marketo instance, the IP reputation is naturally shared with every other tenant. So it doesn’t necessarily point to anything you have done.

At the same time, whatever sender reputation service you’re using is clearly insufficient, as it should be proactively monitoring the IPs you send from.

How have you determined for sure that you didn’t accidentally expand your audience, for example with a purchased list or people who didn’t opt in?

There are a few reasons you might be seeing a sudden increase in bounces due to Spamhaus even though your email practices seem consistent:

• While you may not have intentionally changed your email content, it's possible a recent campaign or email element (like a specific image or link) tripped a filter.
• If you're on a shared IP with other senders, their poor email practices could be impacting your reputation too.
• Occasionally, Spamhaus can have temporary glitches that cause misidentification.

Here's what you can do to investigate further:

• Look at the content of your most recent emails sent before the bounce increase. Are there any elements that might be getting flagged as spammy? Potentially sent to an audience who didn’t opt in/purchased lisr, etc. (as Sandy pointed out).
• See if your domain is actually listed on any Spamhaus blocklists. You can do this through their Domain Block List Lookup Tool https://check.spamhaus.org/.
• If you're not listed but still experiencing issues, you can contact Spamhaus for a removal request https://www.spamhaus.org/resource-hub/delisting/good-bye-blocklist-removal-center-hello-ip-and-domai....

Here are some additional resources that might be helpful:

• Marketo Bounce Management:https://nation.marketo.com/t5/product-discussions/managing-significant-soft-bounces/td-p/305456
• Understanding Marketo Bounce Categories:https://experienceleague.adobe.com/docs/marketo/using/product-docs/email-marketing/deliverability/ha...

By taking these steps to identify the cause and working with Spamhaus if needed, you should be able to get your bounce rate back down.