claws-mail-address-keeper 3.17.4-2 (s390x binary) in ubuntu focal

 This plugin allows saving outgoing addresses to a designated folder
 in the address book. Addresses are saved only if not found in the
 address book to avoid unwanted duplicates.
 .
 Selecting which headers are scanned for keeping addresses is also
 supported, one or several of 'To', 'Cc' and/or 'Bcc'.