That's really too bad. I mean, it's not to say people won't believe you, it's that people have lied before with no screenshots. Though I'm not sure how a dead computer lost your emails, unless you deleted them and saved them in a folder?

For the future, it's best to keep everything just by email and keep all "finished commissions" in a folder. That way you have it if you ever need it. Watching this community has taught me to save things for a couple years. I know it seems too paranoid, but if you ever need it, you'll have proof about everything.