https://learn.microsoft.com/it-it/dotnet/api/system.net.configuration.smtpnetworkelement.port?view=netframework-4.7.2
SmtpNetworkElement.Port Property (System.Net.Configuration) | Microsoft Learn
Gets or sets the port that SMTP clients use to connect to an SMTP mail server. The default value is 25.
property systemportconfigurationmicrosoftlearn