Hi! I have been reading for some days the forum and find several persons that build smtps solutions with for example: -Interspire + PowerMTA -Sendblaster + Postfix -And so on Also, there are other solutions you can use like sendgrid, mailchip, etc. with your own client side mail sender. This kind of solution i already used it on the past. The main problem i have, is that i'm offering the service to other persons/companies and sometimes their mailing databases are not the best. So with the second option (sendgrid, mailchimp, etc) i will surely start having problems with the sending reputation. I often use programs to check the emails databases but most of them are not 100% accurate, the only way to know 100% that a email is working is to send a real e-mail to that account and see if any replies comes back. So being said that i'm on the time to decide what is the best way to accomplish this: 1) Get the best inbox rate possible 2) Avoid having issue with smtp service in case database has not been properly generated and affect the reputation of the sending IP (Maybe this is accomplish with IP rotation right?) 3) Have a good html message generator from the client side mail sender (Since i'm not a HTML designer) 4) Be able to get good tracking information of the emails i send. Note: The amount of emails i send montly can vary from 20K-30K to 100K-120K for example. Thanks for everyone who takes the time to read this on this great community! Regards!