Load balance SMTP traffic to a specific pool member based on the "FROM" mail header

If I may add, you'd likely need nothing less than a full SMTP proxy iRule to make this work, which there are several floating around the forum. The "MAIL FROM" message is not the first message in the SMTP connection, so you'd need to buffer all of the data on the client side first, make your determination, and then forward it to the server. For the purposes of a health check, however, there may be other options. You could, for example, create an external SMTP monitor in Bash that sends an email to each pool member on some regular interval (which would then be configured to automatically log and delete the message). Take a look at this solution article for more on that:

http://support.f5.com/kb/en-us/solutions/public/13000/100/sol13180.html?sr=34155522