I am not sure if this is the efficient way.
But the solution I found if you are searching for the emails with the same body or subject.
After “Get Outlook mail” for each mail then Save Mail Message to a text file and Read text file as shown in the screenshot and the expression used in assign activity would be
System.Text.RegularExpressions.Regex.Match( text ,“(?<=Sentence before specific part).*?(?= Sentence after Specific part)”).ToString