Sean Connor wrote:

Is there any reason to put the message into an attachment?

Yes.  Most people would not want to type in a whole fic into a mail
message, especially when they already have it on their systems as a
file.

The problem stems from the way the mailer handles the attachment.  With
my mailer, I can specify whether the attachment is supposed to be inline
or if it goes as a separate file.  Some mailers just may not be able to
put a text attachment inline.