This can be complicated to integrate, and if you’re using just one IP address then your server could easily be blacklisted.
So while you could use scripts that are hosted on your web hosting accounts or website, this solution can be problematic, especially when you begin to start emailing and people begin to report your IP address as a spammer (even though you are really not a spammer). Ultimately what happens is that your IP address can be blocked and this is problematic simply because when you try to email your list it goes to their spam folder. So, you want to make sure that you avoid this problem and go around this roadblock.
Then at this point most people want to go back to a 3rd party autoresponder service.