Using "Total Pending" attribute to monitor mail router health

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Last week I've been asked to investigate an issue with Domino agent returning unexpected data.
Customer was complaining about wrong values returned for attribute "Total Pending" in "Domino Mail" attribute group.

This value was not matching for most of the server rows when compared with the value
returned for "Pending Mail" by command "show server".
While instead the "Dead" attribute was consistent in both TEP and "show server" output.

Setting specific traces I noticed that the "total pending" attribute, as well as other
attributes in the same attribute groups, are retrieved directly from the Domino
server statistics and agent does not perform any operation over it.

Data showed in TEP for "Total Pending" is consistent with the information retrieved directly from Domino Server Statistics.
"Total Pending" is obtained from field Mail.TotalPending in the Domino Server statistics.
It includes both Dead and Held mail.

So if you have an high value for Dead mail, usually you will have also an high value for Total Pending.
Mail.TotalPending is updated by the server task to reflect the current number of messages that are pending delivery.
Can we rely on it to monitor pending mails ?
The drawback to using  Mail.TotalPending is that it is updated by the server task every five minutes, and thus its value becomes "stale"
and some time may not reflect the current sum of Dead+Held mail.

So generally speaking, you cannot compare the "Pending Mail" value returned by show server with "Total Pending".

Looking at the "Pending Mail" field, it is defined as: "Number of mail documents waiting to be routed to other servers and users."

In the Domino Agent, the attribute Waiting is the one that closely matches the Pending Mail,
as it is defined as "The number of outgoing mail messages currently in MAIL.BOX waiting."

If you want to evaluate the reliability of the values showed by TEP, instead of using show server, you can run a "show stat mail".

In this way you can check if there is really something wrong with data showed by Domino agent.
If you want to keep under control the pending emails, you must decide if you want to consider also the dead mails.
In such case you can use Total Pending attribute, but you need to remember that this value is updated by Domino server every 5 minutes.
If instead you don't want to take dead mails into account, use "Waiting" attribute in the ITM situations.

Some additional considerations from Domino side:
"Mail.TotalPending" may be more reliable than "Mail.Waiting".
Mail.Waiting is dependent on the router task; if the router is not running, then Mail.Waiting is not updated.
As previously wrote, Mail.TotalPending is updated by the server task to reflect the current number of messages that are pending delivery.  The drawback to using  Mail.TotalPending is that it is updated by the server task every five minutes.

Mail.Dead represents mail that cannot be delivered and could not be returned to the sender.
Mail.Hold is mail that is being held pending delivery to an external site.
Mail.TotalPending count includes both Dead and Held mail, while the Mail.Waiting figure does not include these items.
 
The absence of Pending/Waiting mail (i.e. Mail.TotalPending=0, Mail.Waiting=0) is an indication of a healthy mail router.

Hope this helps.

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