==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.4
- Linux/BSD distribution name and version: centos 7 (fully updated)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): installed ldap then changed it to AD DC samba 4.3.4
- Web server (Apache or Nginx): nginx
- Manage mail accounts with iRedAdmin-Pro? NO
- Related log if you're reporting an issue:
====

http://www.iredmail.org/docs/active.directory.html

If you do those step it doesnt work this is because since you integrated iredpd it fails

you got to modify /opt/iredapd/settings.py and change

ldap_uri = "ldap://ad.domain.com:389"
ldap_basedn = "cn=users,dc=domain,dc=com"
ldap_binddn = "vmail@domain.com"
ldap_bindpw = "password"

regards