Mass Mailing Software wanted

Hello Coder, I am looking for a mass mailing software application. I am not able to use an autoresponder service as the leads I have are not registered with any autoresponder service. In times where one is blacklisted being a spammer easily it is needed to get a mass mailing software which guarantees delivery of mails into the mailbox and not into spam. The leads I have are related to my product. So, there is nothing to worry about that. I tried writing e-mails by putting them in manually, but after about 300 sent mails, the mailboxes were blocked. Are you able to help? I am not looking for a mailing service. I would like to have a software that does the mailing. Thank you