Hotmail email delivery failures due to connection limits are commonly linked to poor IP reputation, leading Microsoft to implement throttling. Resolving this involves a multi-faceted approach: closely monitoring IP reputation using SNDS, gradually warming up IPs, reducing the number of simultaneous SMTP connections (potentially starting below 50), pausing sending temporarily (4-12 hours), authenticating emails with SPF, DKIM, and DMARC, maintaining clean mailing lists and removing unengaged subscribers, lowering the overall sending rate, implementing retry mechanisms for throttled emails, utilizing connection pooling to optimize resource use, segmenting mailing lists to prioritize sending to engaged users, closely monitoring bounce messages for deliverability issues, experimenting to determine the optimal connection number, improving sender engagement metrics, and implementing proper queuing and handling of temporary throttling. Consulting specific error messages, adhering to ISP service agreements, and ensuring easy unsubscribe options are also crucial.