I recommend Mail Chimp instead of using your ISP's smtp servers. Mail Chimp is great for small/medium size businesses (and home users) that have a mailing list that is bigger than their ISP's max recipients allow list. Mail Chimp is free to use up to a limit of several thousands of sends per month and there is a counter on your login page so you can see how much usage you have remaining each month. There are a variety of templates available to help you get started too!
Thank you very much Popowich for your very helpful response the other day. mailchimp looks more or less exactly what I have been looking for. I have just made an account with them and will see what I can do with them very soon.
as far as I can see, it seems that with mailchimp and similar mail services you can only send out emails to people who have already subscribed to recieve messages from you.
Being an artist, every now and again I send emails to a list of recipients I have made from searching art gallery websites. None of them have subscribed to any email account I have. The list is of several hundred recipients, but currently I have to divide the list up into groups of 20 per email rather than sending to the entire list in one go, which is what I would like to be able to do. Currently if I exceed 20 the message just gets sent back.
I often get emails from websites and companies that I have never subscribed to so there must be a way of doing it.