feat: add function ValidateHostAndUser to validate host and user preventing SPAN and BOT

[moisespsena]

I'm using the function ValidateHost to validates host and user in my server, bot, my server provider forwarded this alert to me:

This is an abuse report for an email message sent by IP XXX.XXX.XXX.XXX on Thu, 18 Jun 2020 21:16:22 -0300
This abuse appears to be a spoofing attack or its sender has a wrong SPF configuration for sure.
If you have any question about this abuse, contact the anti-spam administrator [email protected].
For more information about this abuse format below, see https://tools.ietf.org/html/rfc5965
Feedback-Type: abuse
User-Agent: SPFBL/2.11
Version: 1
Original-Mail-From: [email protected]
Original-Rcpt-To: [email protected]
Arrival-Date: Thu, 18 Jun 2020 21:16:22 -0300
Reporting-MTA: dns; mx-br.spfbl.net
Source-IP: XXX.XXX.XXX.XXX
Authentication-Results: mx-br.spfbl.net; smtp.mail=[email protected]; spf=softfail
Removal-Recipient: [email protected]
This email message was rejected at RCPT TO command, so we don't have its headers.

I noticed that the email informed in the message was the one set in the ValidateHost function. So, I made the following changes:

1. the ValidateHost function now validates only the host of the email address and no longer the user, since it does not require a valid SMTP domain to return.
2. I created the ValidateHostAndUser function that requires the arguments serverHostName and serverMailAddress.

In this way it makes it possible to validate according to each application and hosting server of the same, not using your pre-fixed email address ([email protected]) and not even a host that did not exist (checkmail.me) .

[badoux]

Thanks for your contribution !