Thanks for reaching out in our Community forums and for sharing your concern, I’d be happy to help.
There can be various causes of receiving this error message. Depending on the performance of your campaign, it could be flagged due to the bounce rate. When an incorrect email message prevents a message from being delivered, then the corresponding email address is automatically removed from the subscriber list. It's important to audit this list and remove any emails that may have a negative impact on the deliverability of your emails. Feel free to check out our help document on email campaign delivery that will go over how to remove subscribers and optimize your list.
If you have any other questions, feel free to follow up and let me know! Additionally, I'm always looking to help out merchants with ideas or feedback related to their stores. How is email marketing going so far? You can check out our guide that covers the Best practices for Shopify Email to help improve your content as well!
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