parse array for valid usernames

I was helping a colleague with a list of email addresses and trying to get a valid username out of it. He is going to get a list of emails every week so writing a script to parse it out for him seemed the best idea. This is only part of the process; there are steps to actually create the account if not already existing and more. So this is mainly an example of text parsing to get the info you want based on a few simple rules.

clear
$emails = "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "Perumel.Aranin.Senthenekrishnin"
$usernames = @()

function Get-Username() {
<#
.SYNOPSIS
 takes a given email address and makes a username based on specific rules
.DESCRIPTION
 Converts a given email address to a username. 
 The username cannot be more than 20 char long, if the first and last name combined are too long only first initial is used
 If the email has a number in it, it is retained in the new username
.PARAMETER
 -email: the email to work with
 -userName: if the email is not parsable, a username can be given to use instead (or in addition to)
.EXAMPLE
 Get-Username -email "[email protected]" -userName "jchinkes"
.NOTES
#>
 Param(
 [Parameter(Mandatory=$True)][string]$email,
 [string]$userName
 )
 $fname = $null
 $lname = $null
 $nameNum = $null
 try {
 #split the email (do we need a test for valid email address?)
 $splitString1 = $email.split('@')
 #take the username of email and split on dot
 $splitString2 = $splitString1[0].split('.')
 
 if($splitString2.Count -le 1){
 #error checking if there is no first or last name
 #is there a better test?
 #use $userName here somehow
 }
 
 if($splitString2.Count -ge 3){
 #more than three items in the array
 if($splitString2[2] -match "^[\d\.]+$"){
 #the third item is a number
 $nameNum = $splitString2[2]
 $lname = $splitString2[1]
 }
 else {
 #third item is a name
 $lname = $splitString2[2]
 }
 }
 else {
 #two part user name
 $lname = $splitString2[1]
 }
 $fname = $splitString2[0]
 
 if($nameNum -ne $null){
 #eval name to see if needs trimming
 if ($fname.get_Length() + $lname.get_Length() -gt 18){
 #trim fname and keep lname
 $fname = $fname.Substring(0,1)
 if ($lname.get_Length() -gt 16){
 #need to trim lname too!
 $lname = $lname.Substring(0,16)
 }
 }
 return "$fname.$lname.$nameNum"
 }
 else {
 if ($fname.get_Length() + $lname.get_Length() -gt 20){
 #trim fname and keep lname
 $fname = $fname.Substring(0,1)
 if ($lname.get_Length() -gt 18){
 #need to trim lname too!
 $lname = $lname.Substring(0,18)
 }
 }
 return "$fname.$lname"
 }
 }
 catch {
 "There was an error- $($_.Exception.Message)"
 }
}


foreach($email in $emails){
 $usernames += Get-Username -email $email
}

$usernames