I deleted all messages from my mail with
mailx d MSGS, and now
mailx shows no mail.
But why does
cat ~/mbox still show all of the supposedly deleted messages?
What version of mailx are you using ? What UNIX/Linux OS are you using ? There are mailx variants.... what is your OS, that might help as well.
Note that I found this in the man page of mailx, not sure this is the issue you are encountering, because afaics, the mailx variant of this man page does not accept the
d switch on the command line, I might be mistaken, though.
Deletion causes the mailx program to forget about the message. This is not irreversible;