Acquia recently sent out an email with the subject line "Update - Cloud API v1 End of Life extended to 1 July 2020". This email went out to applications which had made calls to the Acquia Cloud API v1 endpoint within 30 days prior to that email.
Some customers who do not actively utilize the Acquia Cloud API v1 may have received this email. This is because Acquia's Remote Administration team uses a tool that leverages the API v1 endpoint. As a result, traffic from the Remote Administration tool to the API v1 endpoint created some "false positives" for the report used to generate our customer list. It is worth noting that these RA tools are being migrated to API v2.
If your team does not actively use the Acquia Cloud API v1 and you have the Acquia Remote Administration service, this is likely why you received this email.
If you have questions about this, file a support ticket and our Support teams will be happy to work with you.