EmailValidator checkMX and checkPort

[cebe]

I'd like to discuss the EmailValidator options checkMX and checkPort.

In the current implementation they are very useless as they do not comply to any standard and will fail on valid email adresses.

checkMX currently checks whether an MX is defined. That's fine as a good DNS setup should involve an MX entry even if the MX server is the same server that the A record of the Domain points to but there is no must have for an MX.

checkPort is completely useless as it currently checks whether port 25 is open on the server that's behind the A record of a domain an not behind the MX. If MX is defined it is very likely that there is no port 25 open on the webserver and no MTA will try to deliver to A record when MX is defined.

We should either drop these options or implement them in a better way.
I propose the following changes:

• drop checkMX option
• introduce checkDNSDomain or similar name that checks wether the domain exists in DNS. This is much more useful than checking whether there is MX or not. Note that there is no need for a A record. It should check whether A or MX are defined.
• if we want to keep checkPort feature it should check for MX and then try all MX ports and if no MX defined, the domain itself. As it may be normal for an MX server to be under load and respond slowly I am not sure if this is a good option to test while rendering a web page though. Default timeout is 30sec afaik so this can slow down validation process significantly.

[qiangxue]

I'm fine with what you suggested.

[cebe]

I'd personaly vote for removing the checkPort feature as it has the drawbacks described above.
Opinions @yiisoft/core-developers ?

[DaSourcerer]

What about the code in yiisoft/yii#718?

[cebe]

The code would work but it is about the general idea which is bad imo. Even if the MX is down right now because of temporary error the mail could be delivered in an hour for example.
Mailservers are not ment to be always up. An MX has to retry until a given period if a server is currently not available. I consider it save to take down my MX for a few minutes to do maintainance. No user will ever notice.

[DaSourcerer]

Those are excellent points. But I think it should be left to the user to decide if it's worth the risk. Some people want rigid checks and are ok with some "losses."

Having said this, I think nonetheless DNS and port checking could be improved in the way @cebe described.

[cebe]

As I think those people do not understand what they are doing so they are not really okay with the "losses". Will remove the port checking. If someone really wants to do something like that he can extend the validator but we do not encourage this practise.