How is writing code to send an email any different than sending one manually through Outlook?


25 people in my company donated their personal email addresses for the test portion of a project. As of today about 11 emails were rejected for the following reason:
Code:
The following recipient(s) could not be reached:

      [email protected] on 10/7/2006 1:25 PM
            Could not deliver the message in the time limit specified.  Please retry or contact your administrator.
            <(MY PC NAME).firstads.firstcare.com #4.4.7>

Code:
    Public Sub sendNewMessage(ByVal emailmsg)

        Dim myEmail As New MailMessage

        Dim attachFile As New Attachment("c:\FileName.pdf")
        myEmail.Attachments.Add(attachFile)
        myEmail.To.Add(Me.EmailTo)
        myEmail.From = New MailAddress(Me.EmailFrom)
        myEmail.Subject = (Me.EmailSubject)
        myEmail.Body = Me.EmailBody
        Dim smtp As New SmtpClient("127.0.0.1")
        'Dim smtp As New SmtpClient("mail.company.com")
        smtp.Send(myEmail)

    End Sub