Usually we enable Mailbox auditing to monitor actions taken by mailbox owners, delegates and administrators. But we do not require mailbox audit to be enabled for service accounts which are actually doing genuine operations.

We can configure mailbox audit logging bypass for service accounts which are configured in applications and access mailboxes frequently. This will Reduce the amount of audit log information generated by a service account.

Below steps can be performed to bypass audit for the service accounts:

To check the mailbox audit bypass we can run the below command

Get-MailboxAuditBypassAssociation -identity serviceaccount

The main parameter we need to look is AuditByPassEnabled.

The default value will be false for mailboxaudit enabled and disabled account.

The AuditBypassEnabled parameter controls if the audit logging is enabled or disabled for this account.
When the value is set to $True this account will have the maiboxaudit disabled.
When the value is set to $false this account will have the maiboxaudit enabled.

We can run the below command to bypass the mailbox audit logging for service account.

Set-MailboxAuditBypassAssociation -Identity “service.crm” -AuditBypassEnabled $true

IMP Note:

By default the mailboxaudit logging is not enabled for newly created mailboxes and existing mailboxes.

We can check the mailboxaudit if its enabled or not with the below command.

Get-Mailbox usermbxx | fl *Audit*

The default value will be false like below and the default audit log age limit is 90 days.

Below script can be used to enable bulk maibox audit based on OU level

The Script can be downloaded here – EnableMailboxAudit

##############################################################
# Description:
# This script enables the Mailbox Audit for new mailboxes in your Organization on OU level.
# You need to make them run on a task scheduler on a weekly basis for new mailboxes audit to be enabled.
# You need to mention the OrganizationalUnit in the script where the mailboxes are present.
# You need to mention the CSV location in Export-Csv.
# You need to mention To address From address and SMTPserver(exchangeserver) for sending this report in email.
################################################################

add-pssnapin Microsoft.Exchange.Management.Powershell.E2010 -ea SilentlyContinue
add-pssnapin Microsoft.Exchange.Management.Powershell.Support -ea SilentlyContinue
$mbxs = Get-Mailbox -OrganizationalUnit “mention OU Name” | where { $_.auditenabled -eq $false } | Select Name, DisplayName, UserPrincipalName,SamAccountName,PrimarySMTPAddress
$mbxs | Export-Csv C:\temp\auditlogs\Audit.csv -Encoding UTF8
$mbxs | % { Set-Mailbox $_.SamAccountName -AuditEnabled:$true -AuditAdmin Copy, Create, FolderBind, HardDelete, MessageBind, Move, MoveToDeletedItems, SendAs, SendOnBehalf, SoftDelete, Update }
$mbxs | % { Set-Mailbox $_.SamAccountName -AuditEnabled:$true -AuditDelegate Create, FolderBind, HardDelete, Move, MoveToDeletedItems, SendAs, SendOnBehalf, SoftDelete, Update }

Send-MailMessage -To emailadmin@domain.com -From reports@domain.com -Subject “Audit Enabled for the attached users” -Attachments C:\temp\auditlogs\Audit.csv -SmtpServer specifysmtpserver -Port 25025 -BodyAsHtml -Body “Audit Enabled”

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Thanks 
Sathish Veerapandian