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[Pradeep1210]

Here it is, using LINQ:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim emailGroup As String
    emailGroup = "[email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; " & _
                 "[email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; " & _
                 "[email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]"
 
    'set the max email addresses per batch, and email seperator character
    Dim maxLengthPerBatch As Integer = 4
    Dim emailSeperator As String = ";"
 
    counter(True, maxLengthPerBatch)
    Dim emailBatches = From email In emailGroup.Split(emailSeperator.ToCharArray) _
                       Group email By url = email.Split("@"c)(1) Into email = Distinct() _
                       Select splitted = From em In email _
                            Group em By gnum = (counter() Mod email.Count) \ maxLengthPerBatch Into em = Group _
                            Order By gnum, em _
                            Select emails = Join(em.ToArray, emailSeperator)
    emailBatches = emailBatches.ToList
 
    'now we have all the batches in our emailBatches variable
    'so we can enumerate thru them and send emails
 
    'let's see if it prints correctly in our debug window.
    For Each batch In emailBatches
        For Each item As String In batch
            Debug.WriteLine(item)
        Next
    Next
End Sub
 
'dummy procedure to mimic i++ kind of thing in C#, since vb.net doesn't have one
Private Function counter(Optional ByVal reset As Boolean = False, Optional ByVal resetSeed As Integer = -1) As Integer
    Static i As Integer = resetSeed
    If reset Then i = resetSeed
    i += 1
    Return i
End Function

Pradeep