[WIP] Allow to check multiple defaults ports

[zytzagoo]

Hi, sorry for not replying sooner (been swamped), and thanks for the contribution(s).

I like the general idea behind this, but it could be slow(er) for the (most common) existing use cases in the wild (since it's actually now doing two attempts per domain by default).

If this could be made optional (turned on via public setter or some such), then I'd be wiling to merge it in.

Without going all OOP-y on it (with a bunch of setters and whatnot), we could just check if $connect_ports is an array, and if so, do the dance you're doing in the PR, but if not, use the old way. Then calling code could just set $validator->connect_ports = [25, 587]; before calling validate()?

Ideally, the whole while/foreach $hosts building thingy would be placed in a separate method...

What are your thoughts on this?

If you're not up for doing it this way, I'll probably do it anyway (as soon as I get some spare time on my hands). If it turns out that there's an actual need for this from other users, that might speed things up a bit, but no promises :)

[sadortun]

Hi @zytzagoo, yes, if you check for invalid domains, it might take twice the time, only if :

1. MX is Good
2. Server did not respond on :25 and on :587

But if the server answer on :25 it should not take longer since only the first port will be checked.

I think it should be fairly easy to allow the checks to be done on multiple ports via configuration

[zytzagoo]

This might be up for discussion again now that 1.0 is modernized.

Some notes (to self if nothing else):

• The code implementing it should make sure to not check/connect twice needlessly etc. (there is no check for that in the WIP code above, the $hosts array is just filled and then iterated over).
• MX queries are done for the domain name, regardless of the port number

Whether the extra complexity is worth it, I'm still not sure really...

Ideally, code implementing this lib can set it's own connect port based on its own grouping of hosts and whatnot, and have separate functions for checking groups of emails that require connections on non-default ports etc.