I try both software above and here is some of my thought. Ultramailer Pros: able to verify the email before send, not valid email or unable to verify email will not send out Cons: unable to set the number of email for each SMTP server. Example mandrill only accept 600 email per day or 2000/month, the software can simply send more then 2000 on mandrill in one single campaign without able to limit it. Atomic Mail Sender Pros: able to set the number of email for each SMTP server. Cons: Not able to verify the email before send, all email will send out. I believe it will hurt the SMTP server and get banned faster. Any one had better software to introduce with both pros above?