VS 2010 How to check for existing items in a list of a public structure

Public Structure EmailDetails
        Private _ItemID As ItemId
        Private _from As String
        Private _subject As String
        Private _attachments As List(Of Attachment)
        Public Sub New(ByVal itemID As ItemId, ByVal mFrom As String, ByVal subject As String, ByVal attachments As List(Of Attachment))
            _ItemID = itemID
            _from = mFrom
            _subject = subject
            _attachments = attachments
        End Sub
 
    End Structure
 
    Private _emailDetails As New List(Of EmailDetails)
 
    Public Sub OnAttachmentsFound(ByRef item As Item, ByRef mFrom As String) Handles Me.AttachmentsFound
 
        _emailDetails.Add(New EmailDetails(item.Id, mFrom, item.Subject, item.Attachments.ToList))
 
    End Sub