Please add SMTP setting to accounts

If you are a troll, I'm sure you're getting off on making me recite this, but SPF is a forward DNS record used to manage (allow and deny) the use of envelope sender domains by Internet hosts.

SPF allows the owner of a domain to dictate, to those smtp-receivers who understand SPF, whether mail claiming to be from a given domain may be emitted by the smtp-sender host.  This verification takes place using a variety of lookup methods, including (but not limited to) a hard-coded list of IPs/subnets, a PTR lookup on the connecting IP to match on a PTR pattern, an MX lookup (and corresponding A lookup) on the sender domain, and the inclusion of other domains' SPF records for supplementary lookups.  There is in fact no SPF mechanism that you can add to your domain that prohibits the appearance of that same mechanism in other, unknown domains' SPF records; in other words, you cannot have an SPF record that prevents mail from being emitted by a host that is configured to serve other domains.  

If you have an spf ip4 mech that says that mail from your domain example.com can only come from 1.2.3.4, that says that any other IP address can't send mail from your domain.  It does not mean that 1.2.3.4 cannot also appear in the SPF record for otherexample.com or somerandomdomain.com.  The same goes for any other mechanism.  If you have an SPF ptr mech that says the emitting IP must have a PTR matching example.com, that does not mean that somerandomdomain.com cannot also have a ptr mech with exactly the same requirement. The SPF record cannot say "...and also exclude any host that serves any other domain." And SPF's include mech, as I noted before, specifically is designed to allow sharing SPF mechs across multiple domains (i.e. domains which emit mail from the same hosts).

You are mixing up a method of locking down a domain's smtp-senders to specific hosts with an (imaginary) method that restricts which, or how many, domains a specific host can serve.

If you are sending mail from a given domain, your smtp-sender needs to be permitted by SPF (if there's a record).  Once that's accomplished -- and it certainly needs to be accomplished to deliver mail reliably -- you will not be accused of "spoofing" if you send mail from another domain using the same smtp-sender.  The main reason you will not be accused of "spoofing" is there is no way for the smtp-receiver to know you serve other domains.  But even if there were a source of such information, as long as all DNS and SMTP configs were in order for each domain, the fact that there are multiple serviced domains is immaterial.

Let me teach you what is most essential to reliably send from a given smtp-sender, with or without SPF in play.  You need to pass the HELO-PTR-A roundtrip check.  This means your smtp-sender's IP must have a PTR record.  This PTR record must mach the SMTP HELO hostname the sender uses in its greeting.  The PTR record must have a corresponding A or CNAME record that leads back to the sending IP.  Any failure in any part of the roundtrip will endanger your ability to deliver mail.

One popular mail server product, some time ago, had a major problem with the roundtrip.  See, it allowed you to send mail from multiple domains via the same outbound IP, but it would alter the HELO hostname accordingly.  So if you sent from user@example.com, the HELO would be smtp.example.com.  If you sent from user2@example.com, the HELO would be smtp.example2.com.  One of those e-mails has to fail the roundtrip, because the IP can only have one PTR (practically speaking, smtp-receivers do not parse multiple PTRs). Either the PTR matches one, or it matches the other, but not both.  (The solution, added to the software several years ago, is to bind a single HELO hostname to every IP, regardless of which domain the mail was coming from.) This is one kind of situation which was commonly misinterpreted with the FUD "Oh noes, I can't use the same server to send mail from multiple domains."  The FUD conclusion isn't true at all.  You just have to pass the roundtrip for each e-mail you emit.  If you can't do that, you will have a problem, but that has nothing to do with serving multiple domains.  It has to do with knowing how to configure your systems, and this means you have to know when to replace some software with others. It is not unlikely that your Email2DB server was actually failing the roundtrip and you didn't know what to fix because you are new to this area.

You should stop now -- unless you are just a troll, of course.  I told you I agree with your feature request (though for other reasons) and it's best that you don't try to find any more diagrams.

Ask ISPs providing business e-mail how many outbound gateway IPs they have (it's not one per domain!). I can tell you what configuration an outbound host actually needs to have the best chance of delivery, because I've worked for multiple managed anti-spam companies. But you need to stop spreading FUD first.