mailing is not easy especially now days. big expirience need to be successful just like everything else, now its haard to hit inbox not like years back, today much better security with all mail providers. what you read someone 100% inbox is probably BS. even if you manage to inbox big part of your list still success is not guarantee to make $.
lists quality in this game is what is most important in my oppinion, now ppl are paranoid to click or open anything in emails so you must build trust with them. optin lists are waay much worth than scraped untargeted random country. then we come to servers,software not big deal to setup but when problems start coming with spamhaus you will be changing alot of server/host providers. let say you doing all good mail alot and make money then your cpa refuse pay and say this is traffic from spam because even with optin lists you can be reported by someone and chances are you will.
there are people who made serious big moneys and still do with mailing however it most of time involve illegal things doing and promoting.
everything in this is so much stress but if you deciede to do it my advice and opp would be first first start building lists think few niches give it some time to grow be patient it will be worth later ( buying lists which are probably mailed many times and harvested ones is not good unless you have power to mail millions random mails for example pharma offers which i doubt)
once you collect nice lists mail them yourself only and dont use any service for it. you can find alot tutorials how to setup everything and the list quality will minimize problems that might come in case if used untargeted lists
