There are a number of factors to consider ...
Are the recipients fully opt'ed in ? ie. have u told them during the sign-up process that they could receive emails from you and or business partners?
Is this something you want to run your self or outsource? If you run it as a 'newsletter' type service with relevant updates and 'recommended' upsells in my mind this will work much better then blindly spamming people.
You need to consider that if it's something that's coming from you you may fall fowl of various ISP's spam filters if the emails aren't formatted properly and bounce backs etc. aren't handled right. This would have the cascade effect of possibly hurting u'r initial sign-up process.
Just my
