Dim client As New System.Net.Mail.SmtpClient()
client.Host = "smtp.qq.com"
client.Credentials = New System.Net.NetworkCredential("455189993@qq.com", "helen6849338.")
client.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network
Dim message As New System.Net.Mail.MailMessage()  ----------------这句话错误，啥问题啊？

message.From = new System.Net.Mail.MailAddress("455189993@qq.com")

message.To.Add("2450314695@qq.com")
message.To.Add("2450314695@qq.com")
message.To.Add("2450314695@qq.com")
message.Subject = "邮件测试"
message.BodyEncoding = System.Text.Encoding.UTF8

\'message.Bcc.Add("2450314695@qq.com") \'密送

\'message.cc.Add("2450314695@qq.com") \'抄送

Dim content As String

content &= "这是文字" & vbcrlf
content &= "也是文字"

message.Body = content

Try
    client.Send(message)
    msgbox("发送成功")
Catch ex As Exception
    msgbox("发送失败:" & ex.message)
End Try

这段代码没有问题，请贴出你自己的完整的代码。