Query Mailbox by LegacyExchangeDN

In a large organization with mailbox quotas, you will see an ongoing number of events indicating that users are at the limit of their quotas. In the event log you will see:

Event Source: MSExchangeIS
Event ID: 8528
The mailbox for /o=ExchangeOrg/ou=AdministrativeGroup/cn=Recipients/cn=UserIdentifier 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.

The overall identifier for the mailbox is the LegacyExchangeDN attribute for the user mailbox. Most of the time, you can look at this value and quickly figure out which user is having the issue. If it's a current user, you can wait or contact them. In a large environment, you may not personally know the users, and you can investigate whether this is a disabled account that needs to be removed.

Today I was looking at one of these events and saw that the final UserIdentifier portion of the LegacyExchangeDN attribute was a long GUID number. To find the actual user account I needed to query the mailbox with a filter for LegacyExchangeDN.

Get-Mailbox -Filter {LegacyExchangeDN -eq " /o=ExchangeOrg/ou=AdministrativeGroup/cn=Recipients/cn=UserIdentifier"}

Please note that using the -Filter parameter is much more efficient that doing Get-Mailbox and piping it to Where-Object. Using the -Filter parameter is almost instant whereas piping Get-Mailbox to Where-Object can take several minutes.