主题：使用System.Web.Mail发邮件怎样添加附件？

Dim client As New System.Net.Mail.SmtpClient()
'client.timeout = 1000 '1秒
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
message.From = new System.Net.Mail.MailAddress("455189993@qq.com")
message.To.Add("765427475@qq.com")

'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

Dim attachment As new  System.Net.Mail.Attachment("d:\test.xls",  System.Net.Mime.MediaTypeNames.Application.Octet)
message.Attachments.Add(attachment)

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

finally

    message.Dispose()
End Try

一样可以，加上

client.EnableSsl = True 'SSL

我这样测试没问题

Dim client As New System.Net.Mail.SmtpClient("smtp.qq.com", 587) '或者465
client.EnableSsl = True 'SSL

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()

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

'message.To.Add(new System.Net.Mail.MailAddress("2450314695@qq.com","人名"))
message.To.Add("2450314695@qq.com")
message.Subject = "邮件测试"
message.BodyEncoding = System.Text.Encoding.UTF8

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

参考

https://docs.microsoft.com/zh-cn/dotnet/api/system.web.mail.mailattachment.-ctor?view=netframework-4.7.2#System_Web_Mail_MailAttachment__ctor_System_String_