Identifying all company mail streams and sending tools is crucial for maintaining control over sending reputation, preventing unauthorized sending, and ensuring email deliverability. Key strategies include leveraging DMARC aggregate reports, performing comprehensive email infrastructure audits, reviewing DNS records (SPF, DKIM, DMARC), and using third-party email analysis tools. Auditing internal mail relays, applications, and third-party services is also essential, as is regularly reviewing email sending practices and user accounts. Utilizing email testing tools to analyze email headers helps uncover potential deliverability issues and identifies all mail streams, both legitimate and unauthorized.