Outlook 2002 wont send messages….

I have a problem that is really starting to annoy me. At times I have to write several e-mails in one sitting, so obviously (not on broadband yet!) I write them while I’m not connected. My problem is, whether I am working online or offline accordingto outlook, whenever I connect to the internet to send my mail I get a message back from the ‘system administrator’ stating my mail is undeliverable! I’m running a stand alone computer in my home so I dont know how a system administrator plays any part. Someone please help as I’m getting to the end of my tether….