I've only had a single 4 figure outbound domain sale that went miraculously easy. It was a squadhelp premium, single word with a Z instead of an S (6 letters). Company used domain name Get******.com and it was a perfect upgrade. They recently had a multi-million dollar funding, and I messaged them on Telegram about the domain for sale. It was purchased a couple days later for around $4100. Other than that I have sent thousands of emails to end-users, rarely get replies even on very good domains. I think calling is the way to go. I've had better luck just calling the owners and discussing with them. Still, it will be hard to get 5 figures or more unless it is a super premium single word or high competition two word with many extensions registered. I think it's worth notifying potential end users about domain for sale just to get some eyes or talks going. Still, don't think outbound produces much results for the effort involved.