by

sudo sync
sudo apt-get update
sudo apt-get -y upgrade
sudo apt-get -y dist-upgrade
sudo sed -i /deb/s/stretch/bullseye/g /etc/apt/sources.list
sudo sed -i /deb/s/stretch/bullseye/g /etc/apt/sources.list.d/*.list
sudo apt-get update
sudo apt-get -y upgrade
sudo apt-get -y dist-upgrade
sudo sync

martinrusev

ALL
      All messages in the mailbox; the default initial key for
	ANDing.

ANSWERED
	Messages with the \Answered flag set.

BCC 
	Messages that contain the specified string in the envelope
	structure's BCC field.