[Dovecot] Authentication Failure

[Carlos Mennens]

I am unable to login to my new mail server running Dovecot and Postfix
for some reason. When I check the mail logs, I am seeing:

Nov 11 16:06:29 mail dovecot: imap-login: Disconnected (no auth
attempts): rip=10.1.10.204, lip=192.168.0.200, TLS handshaking:
SSL_accept() failed: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1
alert unknown ca: SSL alert number 48
Nov 11 16:06:36 mail dovecot: auth: Error: pam(carlos,10.1.10.204):
pam_authenticate() failed: Authentication failure (/etc/pam.d/dovecot
missing?)
Nov 11 16:06:53 mail dovecot: imap-login: Disconnected (auth failed, 3
attempts): user=<carlos>, method=PLAIN, rip=10.1.10.204,
lip=192.168.0.200, TLS
Nov 11 16:07:12 mail dovecot: imap-login: Disconnected (auth failed, 3
attempts): user=<carlos at iamghost.com>, method=PLAIN, rip=10.1.10.204,
lip=192.168.0.200, TLS

Below is my configuration file for Dovecot:

# 2.0.7: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.35 x86_64
auth_mechanisms = plain login
mail_location = maildir:~/mail
passdb {
  driver = pam
}
protocols = imap
service auth {
  unix_listener auth-client {
    group = postfix
    mode = 0660
    user = postfix
  }
  user = root
}
ssl_cert = </etc/ssl/certs/mail.crt
ssl_key = </etc/ssl/private/mail.key
userdb {
  driver = passwd
}
protocol imap {
  imap_client_workarounds = delay-newmail tb-extra-mailbox-sep
}

Does anyone know what is causing this error or how I can resolve this?