When in input mode (Receive Mode) or Send Mode:
* If an error is encountered processing an input line beginning
with a <tilde> ('~') character, (see Command Escapes in
mailx), a diagnostic message shall be written to standard
error, and the message being composed may be modified, but
this condition shall not prevent the message from being sent.
* Other errors shall prevent the sending of the message.
When in command mode:
* Default.
The following sections are informative.
