I had opened a thread a while ago in regards to dsync duplicate delivery issues. Here is an update in case anybody else is suffering from this:

https://dovecot.org/list/dovecot/2016-April/103973.html

We are using an LDAP backend for userdb and passdb lookups and this is causing multiple replication users to be created. Here is the broken setup:

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userdb

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hosts = localhost dn = cn=dovecot,dc... dnpass = PASSWORD ldap_version = 3 base = ou=instances,dc... deref = never scope = subtree user_attrs =
=home=/mail/spool/hash-%0.2M{ldap:uid}/%{ldap:uid},
=mail=maildir:/mail/spool/hash-%0.2M{ldap:uid}/%{ldap:maildrop} user_filter = (&(objectClass=mailUser)(uid=%n)) iterate_attrs = uid=user iterate_filter = (objectClass=mailUser) ###############################################

passdsb

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hosts = localhost dn = cn=dovecot,dc=dc... dnpass = PASSWORD ldap_version = 3 base = ou=instances,dc=dc... deref = never scope = subtree pass_attrs = uid=user,userPassword=password,
=userdb_home=/mail/spool/hash-%0.2M{ldap:uid}/%{ldap:uid},
=userdb_mail=maildir:/mail/spool/hash-%0.2M{ldap:uid}/%{ldap:maildrop} pass_filter = (&(objectClass=mailUser)(uid=%n))

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If you don't specify a user attribute in the userdb configuration, dovecot uses the destination email address to create the replication user in addition to users based on the definitions from iterate_attr and pass_attr entries. At the end, multiple replication users are created for the same mailbox causing deleted messages to re-appear and get delivered multiple times.

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username priority fast sync full sync failed buraktest1 none 02:07:02 02:07:02 - buraktest1@buraktest1.domain.com none 02:57:13 02:57:13 - ###############################################

One thing to note here is that the behavior does not manifest itself during the first delivery/retrieval/delete cycle. You need to repeat the cycle again to expose the issue.

The fix is to define and override the "user" attribute in the userdb configuration:

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userdb

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hosts = localhost dn = cn=dovecot,dc... dnpass = PASSWORD ldap_version = 3 base = ou=instances,dc... deref = never scope = subtree user_attrs =
=user=%{ldap:uid},
=home=/mail/spool/hash-%0.2M{ldap:uid}/%{ldap:uid},
=mail=maildir:/mail/spool/hash-%0.2M{ldap:uid}/%{ldap:maildrop} user_filter = (&(objectClass=mailUser)(uid=%n)) iterate_attrs = uid=user iterate_filter = (objectClass=mailUser) ###############################################