LDAP connection: Fatal: Couldn't connect to auth socket

Hello,
first, I want to say thank you that I can join to this forum.

I’m trying to establish an LDAPS connection to my Active Directory and use AD authentication for Roundcube. The reason is that I want to replace MS Exchange.

Has anyone successfully got this combination working?

Certificates have been created and installed.

openssl s_client -connect server.local:636 -showcerts -brief </dev/null

→ “Verification: OK”

The test also works with:

ldapsearch -x -H ldaps://server.local \

-D "cn=ldapread,cn=Users,dc=domain,dc=local" -W \
-b "dc=domain,dc=local" \
"(objectClass=user)" sAMAccountName

However, I can’t get Dovecote to work with Roundcube so that the AD credentials work.

I get the following error message with every test:

sudo doveadm auth test -a /var/run/dovecot/auth-client 'mail@domain.local' 'SECRET'
→ Fatal: Couldn’t connect to auth socket

To my knowledge, dovecot-ldap.conf.ext, /etc/dovecot/conf.d/10-auth.conf, and /etc/dovecot/conf.d/10-master.conf are configured correctly.

Any ideas would be appreciated.

Regards,
Steffen