msdn PostMessage 的 Remark。
Windows 2000/XP: There is a limit of 10,000 posted messages per message queue. This limit should be sufficiently large. If your application exceeds the limit, it should be redesigned to avoid consuming so many system resources. To adjust this limit, modify the following registry key:
HKEY_LOCAL_MACHINE
SOFTWARE
Microsoft
Windows NT
CurrentVersion
Windows
USERPostMessageLimit
The minimum acceptable value is 4000.
To set the message storage size for computers（https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc771767(v=ws.10)）
Click Start, point to All Programs, point to Administrative Tools, and then click Active Directory Users and Computers.
On the View menu, click Users, Groups, and Computers as containers, and then click Advanced Features.
In the console tree, right-click msmq.
Where?
Active Directory Users and Computers/YourDomain/YourOrganizationalUnit (such as Computers or Domain Controllers)/YourComputer/msmq
Click Properties.
On the General tab, in Storage limits, select the Limit message storage to (KB) check box, and then type a maximum total size (in kilobytes) for messages stored in all queues on the selected computer.
Additional considerations
This procedure is not applicable to computers operating in workgroup mode or virtual servers in clusters. To set the computer quota of a workgroup computer create the DWORD registry entry HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSMQ\Parameters\MachineCache\MachineQuota and set to a value of the maximum total size in kilobytes. To change the quota for a virtual server, you need to change the analogous registry key for clustered servers. After setting the registry, restart the Message Queuing service for the changes to take effect.
Warning
Incorrectly editing the registry may severely damage your system. It is recommended that you back up any valuable data on the computer before making changes to the registry.
Following a new installation of Message Queuing, or an upgrade from Windows 2000 or Windows Server 2003, the default limit for these storage sizes is 8 gigabytes (GB).
When the computer quota is reached, no messages can be delivered to any queue or journal on the computer. No negative acknowledgment message is generated, and an error is returned for messages sent locally, while a remote computer tries to resend until the cumulative size of all messages in the queues drops below the specified limit.
消息隊列最大限額說明：
https://support.microsoft.com/zh-cn/help/899612/how-to-set-up-computer-quotas-and-queue-quotas-in-microsoft-message-qu
消息隊列額度設定：
https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc771767(v=ws.10)