set newFileName to (path to temporary items folder from user domain as string) ¬
	& (random number from 10000 to 99999) ¬
	& ".eml"
tell application "Mail"
	set selectedMails to the selection
	if the length of selectedMails is greater than 0 then
		repeat with theMessage in selectedMails
			set newSource to my replaceText("Content-Type: multipart/related;", "Content-Type: multipart/mixed;", source of theMessage)
			set newFile to open for access newFileName with write permission
			write newSource to newFile starting at 0
			close access newFile
			open newFileName
		end repeat
		tell application "Finder" to delete file newFileName
	else
		display alert "Selezionare uno o più messaggi e riprovare"
	end if
end tell

on replaceText(find, replace, someText)
	set prevTIDs to text item delimiters of AppleScript
	set text item delimiters of AppleScript to find
	set someText to text items of someText
	set text item delimiters of AppleScript to replace
	set someText to "" & someText
	set text item delimiters of AppleScript to prevTIDs
	return someText
end replaceText