Asking yourself how many messages are transported in your Exchange organization ?

In my migration scenario for Exchange 2010 I was using Exchange calculator from Exchange team http://blogs.technet.com/b/exchange/archive/2009/11/09/3408737.aspx , and in order to calculate required number of IOPS per database (or server), one of the required input parameters are total messages per mailbox per day and average message size in KB. So, if you don't want just to guess number of total messages per mailbox per day and average message size, you can use Rob's script for gathering email statistics http://gallery.technet.microsoft.com/scriptcenter/bb94b422-eb9e-4c53-a454-f7da6ddfb5d6?SRC=Home . From all the data gathered you can use "Received Total Messages" and "Sent Unique Total" to get Total Number of messages per user. Also, you can use Received MB Total and Sent Unique MB Total to count daily traffic in MB for each user. Using these two parameters you can count average number of total messages per mailbox per day, and average size in MB (KB) for each message and fill in the required parameters in Exchange calculator for Total Send/Receive Capability / Mailbox / Day and Average Message Size (KB).
With small modification of the script you can gather statistics for maximum of 30 days (if you have not changed the default settings for tracking logs history on hub transport servers) and if hub transport server has not hit 1GB of disk space limit. To eliminate so many "ifs" you can use Rob's great script for hub transport message tracking log information : http://mjolinor.wordpress.com/2011/02/11/how-far-back-do-your-message-tracking-logs-really-go/ .