Subscribe by Email and E-Newsletter

Hi,

I'm looking for an email marketing tool to send e-mails for clients offering my products. I did not get the e-mails list from a newsletter tool, I got them from other way.

I want to know if the Subscribe by Email and E-Newsletter garantee that all e-mails will not be sent to spam box. In the subject and email body I already use the best practices to avoid it.

Thanks.