One of our five LDAP slave servers is experiencing issues. We've pulled it out of the cluster and will further investigate tomorrow. While it was misbehaving, you may well have experienced intermittent authentication errors for any applications backed by LDAP auth, including: the web, ownCloud, email lists, etc. This misbehaving node also managed to generate somewhere around 20,000 email message that are still being processed by our problem reporting mechanism. As such, any emails to problem are slightly delayed. They will go through, albeit a bit slower than we would like.
UPDATE (9/10 @ 06:30): Our overnight maintenance software tried to "help" things by re-enabling the errant LDAP server. Unfortunately, it was after we were all in bed, so this went unnoticed until shortly after 6am. It's now been forcibly removed from the cluster until we can track down the root cause.