请高手帮忙，关于发邮件的问题！

[王振凯]

Dim NameS As String
Dim Email As Object
NameS = "http://schemas.microsoft.com/cdo/configuration/"
Set Email = CreateObject("CDO.Message")
Email.Subject = Text1.Text ' //邮件标题
Email.Textbody = Text2.Text '//内容
Email.From = "[e-mail]" ' //发信邮箱
Email.Configuration.Fields.Item(NameS & "sendusing") = 2
Email.Configuration.Fields.Item(NameS & "smtpserver") = "smtp.163.com" '//邮件服务器
Email.Configuration.Fields.Item(NameS & "smtpserverport") = 25 '//端口号
Email.Configuration.Fields.Item(NameS & "smtpauthenticate") = 1
Email.Configuration.Fields.Item(NameS & "sendusername") = "xxxxxx" '//发信账号
Email.Configuration.Fields.Item(NameS & "sendpassword") = "aaaa" '//邮箱密码
Email.To = [e-mail] ' // 收信邮箱
Email.Configuration.Fields.Update
Email.send

在发送成功几次之后就出现：运行时错误'-2147220978 (8004020e)'

该如何解决？请求高手帮忙！