First launch
Open Volim Mail
for the first time.
Build 138 is signed with an Apple Development certificate but hasn’t been notarized yet, so macOS may stop its first launch.
Open it from Finder
Double-click Volim Mail. If it opens, you’re done.
If macOS blocks it
Open System Settings, choose Privacy & Security, and scroll down to Security.
Choose Open Anyway
Click Open Anyway beside Volim Mail, then confirm. You only do this once.
Apple describes this in Safely open apps on your Mac
Stay safe
Only do this for a download you trust.
Use these steps only for a copy you got from the official Volim release page. Don’t turn off Gatekeeper, and don’t use Terminal commands to get around a check.
If macOS says the app is damaged or contains malware, don’t override that warning. Stop, and contact the maintainer through the release page.