According to wiki2.dovecot.org the problem is solved by removing the write persmissions to the group on /var/spool/mail/username.

doveadm replicator status <username pattern>

<username pattern> is something like *@example.com, user@example.com, u* or just *

doveadm replicator dsync-status

Accepts a username pattern as well, but works without it.

doveadm force-resync is not related to replication!

Credits:

• https://wiki.dovecot.org/Replication

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