Hello! I downloaded and opened the app and it looks great! I saw I had 5k+ social and promotion messages so I right clicked and marked all as read. That however crashed the app and even if I open it again it crashes again.
You can reset your cache by running these this in Terminal: rm ~/Library/Containers/com.mimestream.Mimestream/Data/Library/Application\ Support/Mimestream/Mimestream*
rm -rf ~/Library/Containers/com.mimestream.Mimestream/Data/Library/Application\ Support/Mimestream/Attachments