If you have got too many mails to send, dont send themall together at one single shot. All your mails will most certainly end up in the spam or bulk mail folder of the receiptant.

What you could do is, you could send  mails in batches. Send them in batches of 5 10 50 or 100. The idea is not to let mails leave your server in a continious flow for a long period of time.

Use BCC as much as you can. Send mails with 50 or 100 ids in bcc.  Take a break and send another.

Use thunderbird. Dont go for any of those commercially available bulk mailing software. Or just create your own mailing script and put it on your server.