I don’t find the messages, i.e. the e-mails, on the e-mail server. I’ve sent them with DeltaChat MacOS 0.901.0-PREVIEW. They only show up in that app offline.
Afaik they are stored in an IMAP subfolder. The exact path likely depends on your flavor of IMAP. Most every other email client has an “imap folder subscription” option (to show or not show, and fetch or not fetch)
The switch for send copy to self is not implemented in the current version (0.901.0-PREVIEW). Which is not good because the default behavior changed.
But we already fixed that in the upcoming version which comes out soon.