After using my 8700c, I noticed my emails sent to my @mycingular.blackberry.net email address show up instantly while emails forwarded from my GMAIL account take sometimes up to 15 minutes to arrive.
I tried fooling around with the 8700 to see if there is a built in filter, but there isn't. Does anyone out there use more than 1 email address on the Blackberry and if you do, how do you get your email quickly?

I can send all emails to my main mail address, but replying is a nightmare cause i dont know which reply to address to use!

There are several threads on this topic, but I will try to answer your question.

Any e-mail account you have set to forward to your blackberry.net address should arrive instantly to your BB, unless the account in question only forwards in certain intervals.

If you have BIS set up to poll your other e-mail accounts, such as your Gmail account, BIS will poll your other accounts every 15 minutes or so. The only exception to this seems to be Yahoo! mail as there is some sort of arrangement between RIM and Yahoo! that allows for Yahoo! mail to arrive instantly.

All of the above is assuming there are not any issues with the servers on your e-mail accounts or the RIM BIS servers.

Hope this helps.