Warning Event 9327 from MSExchangeSA

In this case Warning Event 9327 from source: MSExchangeSA was logged in Application Event log on Exchange 2010 server responsible for OAB generation by default every day on 5 AM:

Log Name:      Application
Source:        MSExchangeSA
Date:          12/1/2014 5:04:50 AM
Event ID:      9327
Task Category: (13)
Level:         Warning
Keywords:      Classic
User:          N/A
Description:
OALGen skipped some entries in the offline address list '\Global Address List'.  To see which entries are affected, event logging for the OAL Generator must be set to at least medium.
- \Default Offline Address List

By default, event logging for the OAL Generator is set to lowest level. In order to see why some entries are skipped by OAL Generator, event logging level must be set to at least medium. One way to set this requirement is by using PowerShell :

Set-EventLogLevel -Identity "ExchangeServerName\msexchangesa\oal generator" -Level Medium

Setting the logging level to Medium for the OAL generator will produce a lot of events during the generation of OAB. Informational events generated from MSExchangeSA with Event ID 9359 can be safely ignored, but error events with id 9325 are the one that are triggering the event id 9327 from MSExchangeSA. For example:

Log Name:      Application
Source:        MSExchangeSA
Date:          12/25/2014 5:04:03 AM
Event ID:      9325
Task Category: (13)
Level:         Error
Keywords:      Classic
User:          N/A
Description:
OABGen will skip user entry 'John Doe' in address list '\Global Address List' because the SMTP address '' is invalid.
- \Default Offline Address List

John Doe was not having email address, but was having "ShowInAddressBook" property populated. So, in order to fix this behavior, I've created mailbox for this user, and after that immediately disabled the mailbox for this user, and all exchange related properties were cleared from this user.

Now, return (set) the event logging level for the OAL generator to default (lowest) value:

Set-EventLogLevel -Identity "ExchangeServerName\msexchangesa\oal generator" -Level Lowest

And, warning Event 9327 from source: MSExchangeSA was not logged in Application Event log on Exchange 2010 server responsible for OAB generation in 5 AM.