Have you ever lost a deal or a client because an important email landed in spam? What happened?

I've heard stories in the last 4 years as an email deliverability consultant that surprised me and sometimes scared me at the fragility of email, and how easily just one factor can severely hurt your business. Here's a few examples:

• Client who was a recruiter lost 2 deals worth $50K in 2 weeks because their client never saw their email in time because it landed in spam

• Large NetSuite ERP provider had a sales rep sending 50K cold emails a month using Gmass from his primary company email address which tanked the deliverability of the entire company

• Large industrial parts wholesaler had someone spoofing their domain which tanked their deliverability

Curious to hear what some of you have experienced and what you did to resolve it?