Corrections are welcome, and wrong numbers are worth more than kind words.
The Buildsmith Discord is the fastest way to get an answer, to report a wrong number, or to say what the site is missing. Questions asked there help somebody else reading later, which a mailbox never does.
contact@buildsmith.net reaches a person. Use it for anything you would rather not say in public: an account deletion, a subscription problem, a refund within 14 days of subscribing that the button on the account page could not confirm (for subscribers in the EU, the EEA and the UK), or a moderation decision you want looked at again.
For a wrong number, the page it is on and what you believe the right value is. A source helps, and a screenshot from the game helps more. Data here is versioned by patch, so say which patch you are on.
For a bug, what you did and what happened. Builds live in your browser, so the export button on the build planner produces a file that reproduces the problem exactly.
Delete it yourself on the account page: it asks for your password, then removes the account with its saved builds, published builds, likes, reports and subscription records at once. A subscription still set to renew has to be cancelled first, so does one whose last payment failed (PayPal can still collect it), and so does a refunded subscription PayPal has not yet confirmed cancelled, because deleting the account does not stop PayPal charging it. If you can no longer sign in, write from the address the account uses and it will be deleted for you.
Published builds can be reported from the catalog by anyone signed in, which is faster than email. A moderator can hide a build from the catalog; the author keeps their own copy either way. Every moderation action is recorded with who did it, and hiding a build requires a written reason that is kept with the record. If you think a decision was wrong, say so here and it will be looked at again.
This is a fan site. For anything about the game itself, your account or a purchase from Blizzard, contact Blizzard support rather than this address.