the optional bcc lineif enabled in the mailconfig moduleis prefilled with the sender' addresstoosince it' often used this way to retain copy (new in this versionthe body of the reply is initialized with the signature line in mailconfigalong with the original message' text the original message text is quoted with characters and is prepended with few header lines extracted from the original message to give some context not shown in this example and new in this versiontoothe cc header in replies is also prefilled with all the original recipients of the messageby extracting addresses among the original to and cc headersremoving duplicatesand removing your address from the result in other wordsreply really is reply-to-all by default--it replies to the sender and copies all other recipients as group since the latter isn' always desirableit can be disabled in mailconfig so that replies only initialize to with the original sender you can also simply delete the cc prefill if not wantedbut you may have to add addresses to cc manually if this feature is disabled we'll see reply cc prefills at work later pymailgui demo