One person answers these, usually within a couple of days.
The FAQ covers the questions that come up most: why a sender's messages are missing, what "requested" means instead of "unsubscribed", where your password is kept, and what happens to mail you delete.
It helps to include your macOS version, which mail provider you use, and what you expected to happen. If the app misbehaved, attach a diagnostic log: Settings ▸ Advanced ▸ Export Diagnostics writes the app's own recent log entries to a file you can read before deciding whether to send it.
Those logs contain sender addresses and domains, because diagnosing a failed unsubscribe means knowing which sender failed. They never contain message contents or your password.
Email is fine for anything. If you'd rather file it publicly and you have a GitHub account, the issue tracker is open — but it is never required.
Nevermore has no servers and collects nothing; the privacy policy explains exactly what the app touches and what leaves your Mac. Anything you send to the address above is used only to answer you.