We have the same wish. Additionally, a search for all recipients (Sender or CC) and for "subject or entire message" is requested - maybe this is realizable?

This is not configurable but you can change the default search scope and add some new scopes by modifying UIxMailFolderTemplate.wox. Example:

diff --git a/UI/Templates/MailerUI/UIxMailFolderTemplate.wox b/UI/Templates/MailerUI/UIxMailFolderTemplate.wox
index 1905aaec3..f3de9abb8 100644
--- a/UI/Templates/MailerUI/UIxMailFolderTemplate.wox
+++ b/UI/Templates/MailerUI/UIxMailFolderTemplate.wox
@@ -139,9 +139,10 @@
         </md-input-container>
         <md-input-container flex="25">
           <md-select label:aria-label="Search scope">
-            <md-option value="subject" selected="selected"><var:string label:value="Subject"/></md-option>
+            <md-option value="subject"><var:string label:value="Subject"/></md-option>
             <md-option value="from"><var:string label:value="Sender"/></md-option>
-            <md-option value="subject_or_from"><var:string label:value="Subject or Sender"/></md-option>
+            <md-option value="subject_or_from" selected="selected"><var:string label:value="Subject or Sender"/></md-option>
+            <md-option value="subject_or_body"><var:string label:value="Subject or Body"/></md-option>
             <md-option value="to_or_cc"><var:string label:value="To or Cc"/></md-option>
             <md-option value="body"><var:string label:value="Entire Message"/></md-option>
           </md-select>

Thanks for the support and the project! This can be closed, because of https://github.com/inverse-inc/sogo/commit/8642ff9d00d7152588c44980d7c0fbde7f9a3c1f