Fix removal of extra white spaces

vimrc

@@ -124,11 +124,12 @@ nmap <leader>x :w<cr>:!./"%"<cr>
 " Édition rapide de vimrc avec <leader>+e
 map <leader>e :e! ~/.vim/vimrc<cr>
 
-""" Splits {{{
+" Splits {{{
 " Open new split on the bottom part
 set splitbelow
 " Open new split on the right part
 set splitright
+" }}}
 
 " FZF function to list all files on the system {{{
 function! FzfFiles()
@@ -1011,15 +1012,34 @@ au BufWritePost * call ModeChange()
 set list
 "set listchars=eol:⏎,nbsp:⎵,tab:▸·,extends:>,precedes:<,trail:␠
 set listchars=nbsp:⎵,tab:▸·,extends:>,precedes:<,trail:␠
-" Afficher les espaces superflus en gris clair
+
+" Manage ExtraWhiteSpace {{{
+" Display ExtraWhiteSpace (spaces at the End Of the Line) in gray
 highlight ExtraWhitespace ctermbg=darkgray guibg=lightred
 match ExtraWhitespace /\s\+$/
 
-" Auto-remove extra whitespaces before writing the file
+" Function to clean it
-autocmd BufWritePre * :%s/\s\+$//e
+function! CleanTrailingWhitespace()
+" https://stackoverflow.com/questions/6496778/vim-run-autocmd-on-all-filetypes-except
+	" Specific sed command for mail filetype
+	if &ft =~ 'mail'
+		" Want to keep email's signature (begin with "--" + one extra whitespace).
+		" https://stackoverflow.com/questions/45294980/in-sed-how-to-do-a-pattern-substitution-only-when-another-pattern-doesnt-exist
+		:g!/^--/s/\s\+$//g
+		return
+	endif
+	" Default sed command on all other filetypes
+	%s/\s\+$//e
+endfunction
+
+" Call function before saving
+autocmd BufWritePre * call CleanTrailingWhitespace()
+" }}}
+
 " Auto-remove extra ⏎ before writing the file
 autocmd BufWritePre * :%s/⏎\+$//e
 
+
 " Search for 2 whitespaces and highlight it (red and underline)
 set hls
 let g:HLSpace = 1