#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?<="),"
Local $sString = "["Sender", "mail@text.org"]" & @CRLF & _
"[["Sender", "mail@text.org"], ["Date", "Fri, 09 Jun 2017 13:29:22 +0000"]]" & @CRLF & _
"" & @CRLF & _
"[["Sender", "mail@text.org"], ["Date", "Fri, 09 Jun 2017 13:29:22 +0000"], ["Name", "Dude"]]"
Local $sSubst = ":"
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm