在 RFC 2183 (Communicating Presentation Information in Internet Messages) 中，关于 Content-Disposition 的 filename 域有如下叙述:
Current [RFC 2045] grammar restricts parameter values (and hence Content-Disposition filenames) to US-ASCII. We recognize the great desirability of allowing arbitrary character sets in filenames, but it is beyond the scope of this document to define the necessary mechanisms. We expect that the basic [RFC 1521] `value' specification will someday be amended to allow use of non-US-ASCII characters, at which time the same mechanism should be used in the Content-Disposition filename parameter.
Beyond the limitation to US-ASCII, the sending MUA may wish to bear in mind the limitations of common filesystems. Many have severe length and character set restrictions. Short alphanumeric filenames are least likely to require modification by the receiving system.