gnus-cite-attribution-suffix

gnus-cite-attribution-suffix is a variable defined in `gnus-cite.el'.
Its value is

"\\(\\(wrote\\|writes\\|said\\|says\\|>\\)\\(:\\|\\.\\.\\.\\)\\|----- ?Original Message ?-----\\)[ 	]*$"

Documentation:
*Regexp matching the end of an attribution line.
The text matching the first grouping will be used as a button.

You can customize this variable.