Gnesi
A message has a sender, To, Cc, an optional Bcc, a time, and a body. The body may be sanitized HTML. Plain text still sends.
Bcc is visible only to the sender of that message. Other recipients do not see it in the reading pane.
Replies
Reply goes to the other party. If the latest message is from you, reply goes to its recipients, excluding you. Reply all goes to everyone else on the thread.
Files
Compose can attach a file to a new message. A reply in the web app can list a file, but sending that reply currently posts the body only.
What leaves by email
If a recipient is not a Gnesi account, they start with the email they already use. The full message stays on the conversation. The email they receive is a short invite: why Gnesi, the contact type, any offered amount, the kind of message, and a link to gnesi.io. The body is not in that email. When they switch to the Gnesi app, the conversation is already here.