I have been working and have done a lot of R&D on PRTG...
If you are having your mail exchange server and your are worried about its monitoring use PRTG..
Add your Mail Exchange Server on PRTG using SNMP ( Simple Network Management Protocol) or WMI ( Window Management Instrumentation)..there are other ways also to add Window Base Server on PRTG like Remote Probe provided by PRTG only..
Irrespective of Protocol used to add a Mail Exchange Server on PRTG, add Sensors..
Sensors you can add are:
1. MSExchangeIS Mailbox\Average Delivery Time
2. MSExchangeIS Mailbox\Messages Delivered/sec
3. MSExchangeIS Mailbox\Messages Queued for Submission
4. MSExchangeIS Mailbox\Messages Sent/sec
5. MSExchangeIS Mailbox\Messages Submitted/sec
6. MSExchangeIS Public\Average Delivery Time
7. MSExchangeIS Public\Messages Delivered/sec
8. MSExchangeIS Public\Messages Queued for Submission
9. MSExchangeIS Public\Messages Sent/sec
10. MSExchangeIS Public\Messages Submitted/sec
11. MSExchangeIS\RPC Averaged Latency
12. MSExchangeIS\RPC Num. of Slow Packets
13. MSExchangeIS\RPC Operations/sec
14. MSExchangeIS\RPC Requests
15. POP3
16. SMTP
17. POP3 Roundtrip
Maaaan What else you need to monitor about Mail Exchange Server..!!!!
Rgds
MOK