Why there is an additional NOSPAM in this Yasnippet?

[Hongxu Chen <leftcopy.chx@gmail.com>]

Hi all,

   I am using yasnippet but has some problems with it.

   There is a snippet file in the `snippets/text-mode' directory called
   `email', with the full contents below:

    # name: (user's email)
    # key: email
    # --
    `(replace-regexp-in-string "@" "@NOSPAM." user-mail-address)`

So why there is a need to replace the `@' with `@NOSPAM'?

BTW, is there any setting that looks up ONLY the directory I customized?
I am using this one but it STILL additionally uses the snippets insides
`yasnippets/snippets' directory(I am using elpa to manage el packages so
I do not like to remove or modify the snippets directory).

  (setq yas-snippet-dirs "~/emacs.d/snippets")


 Many thanks.

 Hongxu Chen