Email Campaigns

I can’t use an outlook “add-in” due to corporate firewall. I have a series of 15 emails I send to clients over the series of 90 days. Now I’m manually using outlook task series to remind me and then I manually have to send. yuck. How do I automate this so the emails are sent out automatically? I don’t want to have to generate each email and place in outbox to be sent at a later date. any ideas??