Playing Devil's advocate: SMTP has some back-and-forth stateful chatter. With a custom HTTP API, you can authenticate and send an email in a single request. SMTP Pipelining can reduce this problem, but not all libraries support it (e.g. Python's smtplib).
So what ? Is not like you implement the SMTP protocol into your application to send emails. Any language under the sun has a SMTP implementation exposed as a library.
It's slower, which is important when you're trying to push a lot of emails. If you keep the TLS connection open, sending an HTTP request is very fast. Waiting for the roundtrips of that chatter reduces the throughput, especially on higher latency links.
> If you keep the TLS connection open, sending an HTTP request is very fast. Waiting for the roundtrips of that chatter reduces the throughput, especially on higher latency links.
I agree that for a high load of sending email it can be beneficial to use an intermediate service. IMO a local sendmail is still preferred, but I see your point.
However, the Mailit service makes the client wait on the SMTP traffic too [1]. So with this particular service you now have to wait for both SMTP /and/ HTTP communication. Doesn't really speed thinks up :)
However, the Mailit service makes the client wait on the SMTP traffic too [1]. So with this particular service you now have to wait for both SMTP /and/ HTTP communication. Doesn't really speed thinks up :)
That depends, you could host the Mailit service in the same machine as the email server, which your application instances on other machines would call. This could be useful if you have multiple machines but only want to run a single email server.
Why is that? What security does it provide? This very project just demonstrated that you can send pretty much anything in HTTP(S) so any malware (I presume) you're trying to defeat can do the same.
Spam malware can scan IPs to find open SMTP ports to send spam so some ISPs and hosting providers lock down these ports to avoid getting their IPs blacklisted when a compromised host starts sending a bunch of spam through an open relay. I can see this being used to send email out from some restricted hosting providers.
