In light of the spam problem, most email clients now have spam filters installed. These filters catch spam email & either move it to a 'spam folder' or automatically delete it. After spending a great deal of time laboring over your series of autoresponder messages, it would be a shame to find out that the majority of the messages that are sent out end up in the spam folder, or are automatically deleted as spam!
You can avoid this in two ways. First, when anyone signs up to receive information from your autoresponder, have them automatically redirected to a page that gives them instructions for 'white listing' you. Email clients have an actual white list where the owner of the email client can add specific addresses that should never be considered spam.
The other way to make sure that your autoresponder messages get through the spam filters is to check them using one of the various spam checkers that are reachable online. These programs are often web based, and free to use. They check your message for words or phrases that commonly trigger spam filters in email clients. Don't send out any autoresponder messages without doing a spam check first!