To send Terms & Services emails to in-app users without disrupting deliverability, consider alternative channels if email isn't mandatory. Review best practices, check ESP AUP, and consult with your ESP. Implement a separate sending domain or subdomain, segment your audience (starting with engaged users), and warm up IPs for high volume sends. Prioritize email authentication (SPF, DKIM, DMARC) and maintain good list hygiene by removing unengaged users. Continuously monitor your sender reputation via tools like Google Postmaster Tools, adapting to the evolving email ecosystem. Adhere to GDPR compliance and avoid spam triggers in your email content.