Great to hear, Trevor. As a rule of thumb, I keep complete backups of all my emails. This has proven useful on more than one occasion.
Two that spring to mind involve web designers.
Years ago, I worked for a company that provided web optimization services including landing pages. We created one for a web designer as a trial, on the proviso that if it worked, he would pay for the service. Some months later, after the landing page had been on the first page of Google for quite a while, I emailed him to remind him of the agreement. He claimed to have said no such thing; whereupon I forwarded him the email in which he did agree. I heard nothing back from him, so we just deleted the landing page and they went back into the mires of page five or six.
Another fellow was far worse. He abused the landing page system and essentially created a giant link farm, with every page linking back to each other, with vast lists of keywords and sites that just looked like utter rubbish. After some emails, he got into line and cleaned up the link farm, and continued to use the service. He renewed (paid) for another year. The following year, he didn't want to pay again, and claimed that he didn't know he had to renew at all. Once again, I sent through the emails that noted that he had paid for a year already and agreed to continue to pay. Again, nothing came back from him, so we deleted dozens of his sites.
I was told years ago to always send my work email enquiries to my Hotmail address and I was against it for a while as it seemed like too much work, until I realized this is proof that I had done my work. I was lucky that I did it as I would have been in serious kak if I didn't.