Hosting your own email works great until you try to actually send any. [1] But if you send enough, you eventually have to deal with the spam infrastructure. Customers will complain that critical transactional emails ended up in user spam folders. One person too many will accidentally mark one of your mails as spam. Or you'll relaunch some cloud infrastructure and suddenly your IP is one that is on all the blacklists because of some earlier history that you could never have known. Or one of your customers will innocently assume that you are Mailchimp and send a whole bunch of marketing email through your server.
The symptom of any such problem is that email starts falling into the garbage, perhaps silently. But if you are watching your stats like a hawk (a costly and very boring hobby
) - or, much more likely, if your customers start screaming about the very-real high costs of lost email - you will figure that out within a few days, so it might not take more than another day to figure out how to get yourself off the blacklist (a manual process) and how to apologize to customers for the lost email (a manual process). But, if you value your time at in any way, your first encounter with that problem will be your last, because email services are cheap and easy. I have yet to pay for mine; in small quantities Mailchimp, Mailgun et al are free. Indeed, given that low cost, why wait to get burned before you stop playing with fire, even if the fire looks cute and innocent and warm right now?
[1] Actually, I'm lying: A much more serious problem which occurs at any volume is that email is another piece of the security perimeter. Even if mail servers had almost no configuration and a history of bug-free operation - which they do not, I am joking, and the joke is not very funny - one of the basic rules of security is to put as much distance as possible between your data and services which connect to outside machines. Mailgun is free in small quantities and runs outside your entire datacenter. The math kind of does itself.
The symptom of any such problem is that email starts falling into the garbage, perhaps silently. But if you are watching your stats like a hawk (a costly and very boring hobby ) - or, much more likely, if your customers start screaming about the very-real high costs of lost email - you will figure that out within a few days, so it might not take more than another day to figure out how to get yourself off the blacklist (a manual process) and how to apologize to customers for the lost email (a manual process). But, if you value your time at in any way, your first encounter with that problem will be your last, because email services are cheap and easy. I have yet to pay for mine; in small quantities Mailchimp, Mailgun et al are free. Indeed, given that low cost, why wait to get burned before you stop playing with fire, even if the fire looks cute and innocent and warm right now?
[1] Actually, I'm lying: A much more serious problem which occurs at any volume is that email is another piece of the security perimeter. Even if mail servers had almost no configuration and a history of bug-free operation - which they do not, I am joking, and the joke is not very funny - one of the basic rules of security is to put as much distance as possible between your data and services which connect to outside machines. Mailgun is free in small quantities and runs outside your entire datacenter. The math kind of does itself.