dsync(1) on Linux
The text 29b6960c6c61, as Debian 10 (Buster) shipped it.
Dovecot's two-way mailbox synchronization utility doveadm-backup - Dovecot's one-way mailbox synchronization utility
Flags it lists
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-1 -
-A -
-D -
-F -
-N -
-P -
-R -
-S -
-U -
-d -
-o -
-u -
-v