I keep getting "true" statement for the first match of email and the rest all are "False" - vb.net

Question

I am currently doing a program that will detect Email in a text file, i am able to bring out the email, but couldnt validate the email. The validation code is something look like this:
Dim truelist As New ArrayList
For i As Integer = 0 To ListBox2.Items.Count - 1
truelist.Add(ListBox2.Items(i))
Next
For Each item In truelist
Dim result As Boolean
Dim rgx As New Regex("^[_a-z0-9-]+(.[_a-z0-9-]+)#[a-z0-9-]+(.[a-z0-9-]+)(.[a-z]{2,4})$")
If rgx.IsMatch(item) Then
MessageBox.Show(item, "true")
result = True
Else
MessageBox.Show(item, "false")
result = False
End If
Next
and my sample input is :
ys_host#hotmail.com
.kjdsd.#hotmail.com
.as.das.#hotmail.com
~!U#)(!#U#hotmail.com
idgohwoijgw12942149!#hotmail.com
ys_host#hotmail.com
Even though my 1st input the same with last input, but i will get false return from the last input

Answer 1

Your regex does not account for any space, and evaluates the characters from the start of the input (^) to the end ($). As such, any leading or trailing spaces in the input strings would fail to be matched.
Trim() is the VB command that removes spaces at the end or beginning of strings. LTrim and RTrim are specific commands that remove spaces at either end. Source: https://msdn.microsoft.com/en-us/library/microsoft.visualbasic.strings.trim(v=vs.110).aspx; while https://learn.microsoft.com/en-us/dotnet/standard/base-types/trimming indicates that String.Trim() works on whitespaces in general.
You could Trim() the inputs to your ListBox and this should solve the problem. The safer and better way in this context is to Trim() the inputs to the Regex - data validation at the most effective time in the code. The sample code (based on your code) would be:
Dim truelist As New ArrayList
For i As Integer = 0 To ListBox2.Items.Count - 1
truelist.Add(Trim(ListBox2.Items(i))) '*** Changed this line, added "Trim"
Next
For Each item In truelist
Dim result As Boolean
Dim rgx As New Regex("^[_a-z0-9-]+(.[_a-z0-9-]+)#[a-z0-9-]+(.[a-z0-9-]+)(.[a-z]{2,4})$")
If rgx.IsMatch(item) Then
MessageBox.Show(item, "true")
result = True
Else
MessageBox.Show(item, "false")
result = False
End If
Next
The alternative syntax is truelist.Add(ListBox2.Items(i).Trim()).
As an aside, this code is ripe for setting up in a function - enabling re-use. Here is an example of the refactoring:
'[Main function elements ... Include Sub/Function header etc.]
Dim truelist As New ArrayList
For i As Integer = 0 To ListBox2.Items.Count - 1
truelist.Add(Trim(ListBox2.Items(i))) '*** Changed this line, added "Trim"
Next
For Each item In truelist
Dim result As Boolean
If IsValidEmailAddress(item) Then
' Do valid stuff
Else
' Do not-valid stuff
End If
Next
'[Main Sub/Function tail, include End Sub/Function as relevant]
Function IsValidEmailAddress(value as String) as Boolean
Dim rgx As New Regex("^[_a-z0-9-]+(.[_a-z0-9-]+)#[a-z0-9-]+(.[a-z0-9-]+)(.[a-z]{2,4})$")
return rgx.IsMatch(item.Trim()) ' Note use of Trim here for encapsulated data validation.
' encapsulated data validation may or may not be what you want.
End Function