Occasionally, a single domain user account will lock out. The user is not logged in anywhere else as far as I can tell. I can unlock the account in ADUC, but the account will quickly relock itself as if a bad password were being tried multiple times. In order to resolve this, I have been restarting the Microsoft Exchange Active Directory Topology service on the domain controller. This prevents the continued lockout issue for this one user. Is there anything I should be looking at on this account specifically to prevent this from happening in the future? I've already had the user reset his domain password, and I don't suspect that his account is being brute-forced. Is there any explanation as to why restarting the AD Topology service fixes this issue? Is this a known issue and/or is there a permanent fix for this problem that I can implement on an SBS 2011 Standard server?