Email posting

I have a wordpress.org site set up and I am only posting to it through the email posting option. Normally what happens is this – I write an email and send it to the email address listed as the posting email address in the wordpress option menu. I then go to a web browser and call up the http://www.example.com/wp-mail.php page and that will go to my email server and collect the email and post it to my site. Here are my two questions:

1. Is there any way to automatically call the wp-mail.php page every so often (say, for example every hour or every two hours or so)?
2. Even after I write an email to the correct email address and call the wp-mail.php page manually sometimes it reports that there are no new emails in the inbox. I know that this is not the case because I have sent an email recently. Sometimes it takes up to an hour or more before wp-mail.php will recognize the new email. Is this a problem with wp-mail.php, my email server, both, or something else all together?

Thanks SO MUCH to everyone who can help me with this. I’ve been a long time user or wordpress but have never really set up the email posting option and I am trying it out on a new site that I am thinking about. Thanks in advance!