I'm not sure, but aren't you asking for a way to default to a specific email program to SEND iCal Alerts rather than how to designate a specific "Default email READER" for receiving and linking?
I asked the same question on the iCal forum and I still have no answer. I was able to get iCal under OS10.5.8 to SEND alerts via Entourage rather than Mail, but I forgot how I did it ! And now I want to use Outlook to SEND iCal Alerts (in OS 10.7.4) rather than Mail 5.3 and can't seem to manage it.
I have the same problem. OF COURSE I immediate did as fane_j suggested:This solved my questionRe: Change default email program
Mail > Preferences > Default email reader:
However, as soon as I quit Mail 4.6 it goes back to my previous e-mail client, Eudora, which no longer works with my e-mail provider.
There must be a way to fix this using Unix commands in Terminal. Doers anyone know how to do it?