[root@mgmt6 ~]# rpm -qa | grep 389
389-ds-base-1.3.4.0-23.el7_2.x86_64
389-ds-base-libs-1.3.4.0-23.el7_2.x86_64

Verification steps:
1. Setup a RHDS server (stand-alone)

2. Create a user:
[root@serv ~]# ldapadd -x -h localhost -D 'cn=Directory Manager' -w Secret123 << EOF
dn: uid=user0099,ou=People,dc=example,dc=com
givenName: Test
sn: User
loginShell: /bin/bash
uidNumber: 10099
gidNumber: 10099
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: inetorgperson
objectClass: posixAccount
uid: user0099
gecos: Test User
mail: user0099@dev.null
mail: alias@dev.null
cn: Test User
homeDirectory: /home/user0099
EOF

3. Update the mail attribute by deleting all values and add only one value,
   that was previously used, in the same ldapmodify command:
[root@serv ~]# ldapmodify -x -h localhost -D 'cn=Directory Manager' -w Secret123 << EOF
dn: uid=user0099,ou=People,dc=example,dc=com
changetype: modify
delete: mail
mail: user0099@dev.null
mail: alias@dev.null
-
add: mail
mail: user0099@dev.null
EOF

4. Search for entries that have 'mail=alias@dev.null' (i.e. the value that was
   deleted):
[root@serv ~]# ldapsearch -LLL -x -h localhost -D 'cn=Directory Manager' -w Secret123 -b "dc=example,dc=com" mail=alias@dev.null cn

5. Check the entry as returned by step 4:
[root@serv ~]# ldapsearch -LLL -x -h localhost -D 'cn=Directory Manager' -w Secret123 -b "dc=example,dc=com" uid=user0099 mail
dn: uid=user0099,ou=People,dc=example,dc=com
mail: user0099@dev.null

6. Check that dbscan of the mail index db doesn't show both values:
[root@serv ~]# dbscan -f /var/lib/dirsrv/slapd-serv/db/userRoot/mail.db | grep ^=
=user0099@dev.null 

Marking as VERIFIED.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2016-0204.html