When you supply DataTable in Verify(DataTable, String) call, MailBee uses that DataTable and makes it available in this event handler with Table property. When you supply a string array as the data source (using Verify(String) call), MailBee builds Table from the input string array. Anyway, during the bulk check, MailBee goes through the DataTable picking up data rows one-by-one and getting e-mail addresses from there.
If the input is a string array, the row will contain a single column named "email".
When the input is IDataReader rather than DataTable, this property is a null reference (Nothing in Visual Basic).