Avoid doing it yourself if at all possible.
Companies where users have voluntarily subscribed to email newsletters just about all use third parties to send them out. That's to avoid being falsely identified by the ISPs automated spam systems as a "spammer" and having their domain names and/or email addresses blacklisted. Plus most major ISPs (Telus, Shaw, etc) have clauses that they will automatically cancel your service if the automated systems decide that you're spamming.
That's why all the real spammers that drive us crazy all go to great lengths to hide who they really are. I.E. The real newsletters that people want don't get through but all the real spam does!
If you have a small number to send, then send them yourself manually and in small groups and on different days. Also make sure that you continually change the content a little bit (or personalize them) so that the automated spam detection systems don't see you sending out the same email message over and over again.
Hope that helps!