As per mmsg(7) file names can also be passed as arguments. However, it is presently not checked explicitly whether the specified files actually exist. As such, mblaze utilities exit with a zero exit status even if the specified mail doesn't exist. For example:

$ mblaze -s /does/not/exist
$ echo $?
0

In such cases, an error should be printed and the utility should exit with a non-zero exit status. As briefly discussed on IRC, there is not technical reason why it's presently implemented like that it's just that noone has implemented the proper error handling so far.