The first two options will produce an alert sound if any infected files are found and also whenever a scan completes. This allows you to go away and do something else not pay too much attention to ClamXav while it's doing its thing.
Scan email content…
Most email clients will store email messages and mailboxes in a format called "mbox". What this option does is allow ClamXav to scan the actual contents of individual email messages for embedded virus attachments. This option frequently flags up emails which other email scanners may have missed.
Turning this option on does not mean that ClamXav will automatically scan all of your email - you still need to specify where your email sits by pointing ClamXav at the appropriate folder.
With quarantine setting off (see next section), this option lets you see if an infection exists in your email, leaving you to look through your mailbox and delete the offending message manually. There is a "sticky" thread in my forums explaining various ways to do this. If you use Apple's Mail program (this may affect others too), you must quit every time you delete something from a mailbox otherwise the change will not actually take effect and the infection will still be found. Similarly, if you use Eudora you must compact the mailbox after deleting an infected message.
I advise that you should not use this option in conjunction with the "Quarantine" or ClamXav Sentry's "Delete" option as you may end up with undesirable results.
There is a discussion on my online forums explaining how to get Apple's Mail program to scan each message as it arrives in your mailbox.
Update virus definitions on launch
Virus definitions are small snippets of code which enable ClamXav to detect malware and viruses and must be kept up-to-date for ClamXav to be effective. These definitions are updated very frequently, sometimes as often as twice a day. This option should be enabled to obtain these updated code snippets every time you use ClamXav.
Check for ClamXav update on launch
This option allows ClamXav to ensure the application itself is always up-to-date. Unlike older versions of ClamXav which merely directed you to the website and made you update manually, version 2.0 and higher make use of Sparkle to automate the entire update process within ClamXav itself. All you need to do when an update is available, is hit the "Install Update" button.
If you opt to "include anonymous system profile information", it will tell me what hardware (iMac, Mac Pro, PowerMac etc) and version of Mac OS X your computer is using, and it will enable me to ensure my time and resources are spent supporting the most commonly used combinations and ensure that future versions of ClamXav are better supported.