Duplicate contacts are inserted if the supplied email address is too long for Zoho
When I insert new contacts via the API it doesn't insert a new contact if one exists with the same email address. This is good.
If I insert a new contact where the email address is longer than the allowed length (100 characters), Zoho truncates the email address to 100.
If I then attempt to insert the same email address that is > 100 characters, the API inserts a duplicate. I think it must be comparing the email that isn't truncated versus the truncated version, and therefore decides it isn't a duplicate.