mm-charset-synonym-alist

mm-charset-synonym-alist is a variable defined in `mm-util.el'.
Its value is

((ibm866 . cp866)
 (unicode . utf-16-le)
 (ks_c_5601-1987 . cp949)
 (windows-31j . cp932)
 (utf8 . utf-8)
 (iso8859-1 . iso-8859-1)
 (iso_8859-1 . iso-8859-1))

Documentation:
A mapping from unknown or invalid charset names to the real charset names.

See `mm-codepage-iso-8859-list' and `mm-codepage-ibm-list'.