As having been on both sides of the relationship building effort, my vote would be for just email: quick, scrappy and personal. For example Taylor from Focusma

As having been on both sides of the relationship building effort, my vote would be for just email: quick, scrappy and personal. For example Taylor from Focusmate once reached out to core users by just saying „hey, it‘s me, Taylor, not a marketing person, I‘m building this thing and you seem to be using it a lot, do you have any feedback?“ Interestingly enough, this approach was as rare as effective: I just gave him some and he thanked me. I just wondered why not more people did simple stuff like this.