If you notice that some but not all mail is consistently going missing (only at certain providers, certain addresses showing alternating missing and inboxing/spam results, etc.):

• Ensure you are sending to the complete seed list.
• If using an X-header matching ID, ensure you are not changing the X-header value mid-deployment.
• Contact your email service provider (ESP) to ensure no Everest seed addresses are being suppressed. This could be occurring in the ESP’s interface or in some way that may not be immediately visible.
• If applicable, consult your bounce logs for the associated bounce codes and consult the documentation at that mailbox provider.