I wouldn't recommend Warmbox in case you really don't wanna end up in spam folder.
I was using this tool for two month and it was saying everything is fine, 0% spam.
However the first email I sent to myself landed in spam folder. Then I checked my email with another tool and 57% out of all emails landed in spam! Therefore I was having useless email-campaign for a month prior that.
Warm-up didn't work at all, maybe made it worse. Also it exchanges emails exclusively with gmail-accounts, no yahoo or corporate emails.
Support usually replies on the next day. I got refund for the second month, so thanks for that at least.