Thanks for the reply - sadly this setup doesnt quite work for me as basically I have batches of 100 email addresses. I am using the search API to find email addresses using the IN filter, but this only searches the primary email.
If I also want Contacts via their hs_additional_emails field I have to supply more filters where the field CONTAINS the email. Due to the limitations of the API I can’t really constructs the query I need - unless I am doing it wrong.
For simplicity, imagine you have 1000 users on your system - how do you find them in batch using the API? You need to search both the email field and the additional email comma separated list.