REGEX check to see if a given Email address is valid

Approve-MailAddress.ps1

#region License

<#
	{
		"info": {
			"Statement": "Code is poetry",
			"Author": "Joerg Hochwald",
			"Contact": "joerg.hochwald@outlook.com",
			"Link": "http://hochwald.net",
			"Support": "https://github.com/jhochwald/MyPowerShellStuff/issues"
		},
		"Copyright": "(c) 2012-2016 by Joerg Hochwald & Associates. All rights reserved."
	}

	Redistribution and use in source and binary forms, with or without modification,
	are permitted provided that the following conditions are met:

	1. Redistributions of source code must retain the above copyright notice, this list of
	   conditions and the following disclaimer.

	2. Redistributions in binary form must reproduce the above copyright notice,
	   this list of conditions and the following disclaimer in the documentation and/or
	   other materials provided with the distribution.

	3. Neither the name of the copyright holder nor the names of its contributors may
	   be used to endorse or promote products derived from this software without
	   specific prior written permission.

	THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
	IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
	AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
	CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
	SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
	OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	POSSIBILITY OF SUCH DAMAGE.

	By using the Software, you agree to the License, Terms and Conditions above!

	#################################################
	# modified by     : Joerg Hochwald
	# last modified   : 2016-03-16
	#################################################
#>

#endregion License

function global:Approve-MailAddress {
<#
	.SYNOPSIS
		REGEX check to see if a given Email address is valid

	.DESCRIPTION
		Checks a given Mail Address against a REGEX Filter to see if it is RfC822 complaint
		Not directly related is the REGEX check. Most mailer will not be able to handle it if there
		are non standard chars within the Mail Address...

	.PARAMETER Email
		e.g. "joerg.hochwald@outlook.com"
		Email address to check

	.EXAMPLE
		PS C:\> Approve-MailAddress -Email:"No.Reply@bewoelkt.net"
		True

		Checks a given Mail Address (No.Reply@bewoelkt.net) against a REGEX Filter to see if
		it is RfC822 complaint

	.EXAMPLE
		PS C:\> Approve-MailAddress -Email:"Jörg.hochwald@gmail.com"
		False

		Checks a given Mail Address (Jörg.hochwald@gmail.com) against a REGEX Filter to see if
		it is RfC822 complaint, and it is NOT

	.EXAMPLE
		PS C:\> Approve-MailAddress -Email:"Joerg hochwald@gmail.com"
		False

		Checks a given Mail Address (Joerg hochwald@gmail.com) against a REGEX Filter to see
		if it is RfC822 complaint, and it is NOT

	.EXAMPLE
		PS C:\> Approve-MailAddress -Email:"Joerg.hochwald@gmail"
		False

		Checks a given Mail Address (Joerg.hochwald@gmail) against a REGEX Filter to see
		if it is RfC822 complaint, and it is NOT

	.OUTPUTS
		boolean

	.NOTES
		Internal Helper function to check Mail addresses via REGEX to see if they are
		RfC822 complaint before use them.

	.INPUTS
		Mail Address to check against the RfC822 REGEX Filter

	.LINK
		Joerg Hochwald: http://hochwald.net

	.LINK
		Support https://github.com/jhochwald/MyPowerShellStuff/issues
#>

	[CmdletBinding(ConfirmImpact = 'None',
				   SupportsShouldProcess = $true)]
	[OutputType([bool])]
	param
	(
		[Parameter(Mandatory = $true,
				   HelpMessage = 'Enter the Mail Address that you would like to check (Mandatory)')]
		[ValidateNotNullOrEmpty()]
		[Alias('Mail')]
		[System.String]$Email
	)

	BEGIN {
		# Old REGEX check
		Set-Variable -Name "EmailRegexOld" -Value $("^(?("")("".+?""@)|(([0-9a-zA-Z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-zA-Z])@))(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,6}))$" -as ([regex] -as [type]))

		# New REGEX check (Upper and Lowercase FIX)
		Set-Variable -Name "EmailRegex" -Value $('^[_a-zA-Z0-9-]+(\.[_a-zA-Z0-9-]+)*@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*(\.[a-zA-Z]{2,6})$' -as ([regex] -as [type]))
	}

	PROCESS {
		# Check that the given Address is valid.
		if (($Email -match $EmailRegexOld) -and ($Email -match $EmailRegex)) {
			# Email seems to be valid
			return $true
		} else {
			# Wow, that looks bad!
			return $false
		}
	}
}