We recently had a very strange situation that I felt warranted a post on the forum. In my troubleshooting I had read various other posts referencing this error, but everything those articles suggested checking was set up correctly. To break down the situation, I first began noticed the following error: Log Name: Application Source: MSExchangeFBPublish Date: 5/4/2010 6:10:37 AM Event ID: 8207 Task Category: General Level: Error Keywords: Classic User: N/A Computer: xxx.xxx.com Description: Error updating public folder with free/busy information on virtual machine xxxxx. The error number is 0x80004005. I received these errors for some time (months, and yes that is a long time, but when only a few clients connect via this method, it was not a major issue). Eventually I began receiving the following two errors. Log Name: Application Source: MSExchangeIS Mailbox Store Date: 5/3/2010 8:53:44 PM Event ID: 1022 Task Category: Logons Level: Error Keywords: Classic User: N/A Computer: xxx.xxx.com Description: Logon Failure on database "xxx\xxx" - Windows account xxxx\xxx$; mailbox /o=XXX/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=XXXX/cn=Microsoft System Attendant. Error: 1245 Client Machine: XXXX Client Process: edgetransport.exe Client ProcessId: 0 Client ApplicationId: Client=Hub Transport Log Name: Application Source: MSExchangeIS Date: 5/3/2010 8:40:55 PM Event ID: 8528 Task Category: General Level: Warning Keywords: Classic User: N/A Computer: XXX.XXX.com Description: The mailbox for /o=XXX/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=XXXX/cn=Microsoft System Attendant has exceeded the maximum mailbox size. This mailbox cannot send or receive messages. Incoming messages to this mailbox are returned to sender. The mailbox owner should be notified about the condition of the mailbox as soon as possible. After doing some research I found that when posting Free Busy info to public folders Exchange 2007 will utilize the System Attendant mailbox to post the items to the public folder. Putting two and two together I realized that the cause of the System Attendant mailbox filling up, and therefore disabling itself, was the fact that our environment was not able to post Free Busy (or OAB v4 generation) to public folders. I call to MS was placed to help resolve the issue. 3 weeks later, we have our resolution. We have a unique Exchange environment... by design. We have a couple clustered mailbox servers. Since clustered mailbox servers cannot also contain a public folder store, we also configured two seperate mailbox servers to contain our public folder DBs. To avoid confusing our Operations team who handles configuring Exchange mailboxes for our users, we decided we did not want to also create a private mailbox store on the server designated as the public folder (mailbox) server. This means there are no SA mailboxes on these particular servers as there is no Mailbox DB in existence on that server. The fix was simple in the end, but took a long time to figure out. We had to create a mailbox database on the public folder mailbox servers. Once this DB was created, the system automatically created the SA mailbox on the public folder servers. Shortly after that we were able to verify that the SA mailboxes on the mailbox servers in question cleared themselves out, free busy info was able to publish to public folders, and the OAB generation process was able to create the appropriate folders it needed. All the errors have since cleared out and things are running normally.