feat: Remove echo from passthrough recipients

Author: cliffmccarthy

chatmaild/src/chatmaild/ini/chatmail.ini.f

@@ -43,7 +43,7 @@
 
 # list of e-mail recipients for which to accept outbound un-encrypted mails
 # (space-separated, item may start with "@" to whitelist whole recipient domains)
-passthrough_recipients = echo@{mail_domain}
+passthrough_recipients =
 
 # path to www directory - documented here: https://chatmail.at/doc/relay/getting_started.html#custom-web-pages
 #www_folder = www