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Hi

You can use any port - the listed ports are the ones used by default and 2525 is a common alternative TLS port.

Port 465 as I recall is usually related to older versions of TLS. So it can be a TLS related issue. Can you tell something about the SMTP provider - and what version of TLS it uses?

Thanks, Nicolai

Hi Nicolai,

Thank you for the clarification.

The SMTP provider uses TLS 1.2 and 1.3.

Best regards,
Abhineet Nayak

Hi 

The port you are using indicates that you use TLS 1.2 which is not supported by .NET Core. From the .NET documentation:

The SmtpClient class only supports the SMTP Service Extension for Secure SMTP over Transport Layer Security as defined in RFC 3207. In this mode, the SMTP session begins on an unencrypted channel, then a STARTTLS command is issued by the client to the server to switch to secure communication using SSL. See RFC 3207 published by the Internet Engineering Task Force (IETF) for more information.

An alternate connection method is where an SSL session is established up front before any protocol commands are sent. This connection method is sometimes called SMTP/SSL, SMTP over SSL, or SMTPS and by default uses port 465. This alternate connection method using SSL is not currently supported.

So check if your SMTP provider supports TLS 1.3 - it is probably another port, and probably 587. You can also try to remove the port from DW configuration and just check the TLS option - or see if it works without TLS at all on port 25.

BR Nicolai