SMTP without NTLM Protocol

GemBox.Email
1

Hi,
for security reasons we are about to switch off NTLM-Protocol in our Network.

In my projects I was using System.Net.Mail to send SMTP Emails

SmtpServer.Port = 465
SmtpServer.Host = “smtp-server”
SmtpServer.UseDefaultCredentials = True
SmtpServer.EnableSsl = True

this does not work when NTLM-Protocol is disabled.

I’am using a licenced Version of GemBox V1.3 in other Projects is there, or in a newer Version, an ability to send Emails without enabled NTLM?

Thank you for response
Frank

2

Hi Frank,

GemBox.Email’s SmtpClient doesn’t have UseDefaultCredentials, so it shouldn’t be affected by disabled NTLM protocol.

The SmtpAuthentication enum lists the supported SMTP authentication mechanisms (such as basic username+password or OAuth 2.0 authentication).

Regards,
Mario

3

Hi Mario,
thank you for this hint.

I got this in place but is does not work relaiable. Maybe you have an idea how this could happen.

There is no difference if I use the 1.3 or 1.7 version of the GemBox-DLL.

There is also no difference if I use
Dim validationDelegate As RemoteCertificateValidationCallback
or
Dim ignoreCertificate As System.Net.Security.RemoteCertificateValidationCallback

I am using the following:

Dim security = GemBox.Email.Security.ConnectionSecurity.StartTls
Dim Port = 465

The HTML-Body is always the same:
HTML = HTML + “” + vbLf
HTML = HTML + “<span style=” + Chr(34) + “font-weight bold;” + Chr(34) + “>Hallo Test im HTML Format ” + vbLf
HTML = HTML + “”

message.BodyHtml = HTML

’ Set the SMTP host, port and connection security.
Using smtp As New SmtpClient(host, port, security, validationDelegate)

smtp.Connect()
AddHist("successful SMTP connect")
smtp.Authenticate("domain\user", PW)
AddHist("authenticated.")
' Send message
smtp.SendMessage(Message)
AddHist("message send successfully.")
smtp.Dispose()

It works a few times not, then it it works for one time. I tryed it out at 3 different Clients, two with disabled NTLM one with NTLM enabled, on all Clients the same effect.

The network traffic passes the Firewall between the Exchange Backend and the Clients unhindered.

Error Message is:
MAIN:5.7.60 SMTP; Client does not have permissions to send as this sender
bei GemBox.Email.Smtp.SmtpClient.SendMessage(MailMessage message)

4

Hi,
I got the issue fixed, our Exchange-Load-Balancer was / is the Problem. It seems so that not all balanced Machines are providing the same Services.

Thank you for your prompt Support

Best regards
Frank