Newsletter slow sending - delay between 2 mails to the same server / max e-mails per hour?

I have to make a newsletter sending utility application which will collect the list of subscriber from our central database and send out the newsletter. I've considered the possibility to be blacklisted due to flooding if I just flush out all emails at once, so I decided to go on a desktop-based softwer which will email those slowly.

my question is

• what is the max emails per hour that may be addressed to the same email domain (recipient/incoming server)?
• or what should be delay between 2 e-mails to the same server for it doesn't consider it flooding?

whichever of the above applies more appropriate to the real-world of mail servers configuration...

thanks

I've implementing sending to max 600 e-mails per recipient domain. That seems to be working fine for some time now and sounds like an OK solution.

Still, some SysAdmin insight on this would be appreciated.