Deleting mail from my email server using the iPhone.

I checked out the iPhone email program on the iPhone. It was very easy to set up my personal email account. Retrieving, and reading emails was easy and beautiful. However, when I deleted the messages I had read, I could not figure out how to also delete them on my email server, which means, that when I come home to my main computer, my email program will again download all the messages I had already read and deleted.

I am curently using a Palm TX, which works just fine for email (text only). The convenient thing I can do is, that when I delete an email message on the Palm, I am presented with a choice to delete the email in question on the device only, or also on the server.

And when I have read all my emails, and empty my trash on the Palm, I am asked, if I want to sync with the email server, and delete the messages from the server also. So when I get home, I only have to deal with new messages and the messages I read before, but did not delete from the server.

I was told by a sales person at the Apple store, that this is how it is on the iPhone, and that you cannot delete messages on your email server from the iPhone.

Is that true, or is there a way to delete emails from the email server?

Thanks in advance for any responses.