系统性能问题。网邮政

我在从应用程序发送邮件时遇到了一个不同寻常的问题。起初它不起作用(无法转发错误垃圾),总之我添加了正确的身份验证,它起作用了。我现在的问题是,如果我尝试发送大约300封电子邮件(每封都有500k的附件),应用程序在整个过程中大约95%的时间都会挂起。

下面是我的一些代码,用于发送每封邮件

 Using mail As New MailMessage()
            With mail
                .From = New MailAddress(My.Resources.EmailFrom)
                For Each contact As Contact In Contacts
                    .To.Add(contact.Email)
                Next
                .Subject = "Accounting"
                .Body = My.Resources.EmailBody
                'Back the stream up to the beginning orelse the attachment
                'will be sent as a zero (0) byte file.
                attachment.Seek(0, SeekOrigin.Begin)
                .Attachments.Add(New Attachment(attachment, String.Concat(Item.Year, Item.AttachmentType.Extension)))
            End With
            Dim smtp As New SmtpClient("192.168.1.2")
            With smtp
                .DeliveryMethod = SmtpDeliveryMethod.Network
                .UseDefaultCredentials = False
                .Credentials = New NetworkCredential("username", "password")
                .Send(mail)
            End With
        End Using
        With item
            .SentStatus = True
            .DateSent = DateTime.Now.Date
            .Save()
        End With
        Return

我在想,我能不能先准备好所有的邮件,然后把它们添加到一个集合中,然后打开一个SMTP会话,然后重复这个集合,像这样调用send

Using mail As New MailMessage()
 ...
MailCollection.Add(mail)

End Using

...

                Dim smtp As New SmtpClient("192.168.1.2")
                With smtp
                    .DeliveryMethod = SmtpDeliveryMethod.Network
                    .UseDefaultCredentials = False
                    .Credentials = New NetworkCredential("username", "password")

                     For Each mail in MainCollection
                          .Send(mail)
                     Next

                End With