X eXtension field Extension fields are used to carry additional RFC822
type lines. X fields contain the X byte followed by
the RFC822 field name, a colon, a space, and the value.
-Z Separator If there are MIME attachments following the message
- text, the Z field specifies the separator string.
+Z Boundary If there are MIME attachments following the message
+ text, the Z field specifies the boundary string.
EXAMPLE