The collective responses from email experts, marketers, and official documentation sources suggest that there are no specific, hard-coded pixel width or subject line character limits that directly cause Microsoft to mark emails as spam. Deliverability is determined by a more holistic approach, involving factors like user engagement (opens, clicks, complaints), sender reputation, content quality, proper HTML formatting, and email rendering across different devices. While specific limits aren't enforced, exceeding common screen widths or using poor HTML can lead to rendering issues, negatively impacting user experience, and potentially increasing the likelihood of emails being marked as spam.