Best Emailing software?

i want to run my first email campaign for a health site and wanted to know what the best overall software is?
im assuming ill be running this from a mail server that allows 5k - 10k emails a day?
where can i go to read up and get caught up to speed?
thx

Interspire is great, I've used it at work and it's really powerful. Need a hand?

one more vote for interspire or oem pro or u can use any simple email application who can send emails via smtp 5k - 10k not very huge