Hi, Yes, this counter really has a known issue related to incorrect caculate. Form my perspective you can ignore it. Thanks.Rowen TechNet Community Support

Thanks Rowen. Is there any article/kb about this known issue that I can refer to? I'd like to remove it from the policy :)

Thank you all. I thought the same... but it's been bothering me as the counter shows the same high numbers for different databases located at different disks multiple times every hour. BTW, We are not running load generator. We also noticed this issue w/ different exchange server when we deployed a policy to watch this counter. I wonder if there is any knows issues with the counter itself.

We see high numbers occasionally for this counter (10 seconds to 30min) on 2007 Exchange servers. Is this counter reliable? We dont have any problems in terms of delivering messages to the mailboxes while the counter shows trouble with the delivery... and IO sec/read and sec/write seems fine.

The System Monitor counter Average Delivery Time in the MSExchangeIS Mailbox performance object will be incorrect when you run Exchange Load Generator. This counter includes delivery times for messages that were delivered during Initialization. Delivery Time is the time, in milliseconds, between an Exchange server receiving the message from the client, and an Exchange server delivering the message to a mailbox. If you have the counter saying 30+ minutes but you receive email as quickly as normal I'd say you probably can disguard this as a false alarm.Jesper Bernle | Microsoft Community Contributor 2011 Awardee

Hi, I think you can try to contact Microsoft support and they might have some workaround. Haven't found informative article for you. Sorry for that.Rowen TechNet Community Support

Hi, Yes, this counter really has a known issue related to incorrect caculate. Form my perspective you can ignore it. Thanks.Rowen TechNet Community Support

Hi, The System Monitor counter Average Delivery Time in the MSExchangeIS Mailbox performance object will be incorrect when you run Exchange Load Generator. This counter includes delivery times for messages that were delivered during Initialization. Delivery Time is the time, in milliseconds, between an Exchange server receiving the message from the client, and an Exchange server delivering the message to a mailbox. For Initialization messages, the time that an Exchange server received the message from the client is the timestamp from the original archived message. Therefore, the delivery time for Initialization messages will frequently be more than one year. Because Initialization message delivery times are included in the Average Delivery Time counter, the average will be incorrect.Rowen TechNet Community Support