<PackageReference Include="System.Security.Permissions" Version="10.0.0-preview.5.25277.114" />

SmtpPermissionAttribute

Controls access to Simple Mail Transport Protocol (SMTP) servers.
using System.Security; using System.Security.Permissions; namespace System.Net.Mail { [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method, AllowMultiple = true, Inherited = false)] public sealed class SmtpPermissionAttribute : CodeAccessSecurityAttribute { public string Access { get { return null; } set { } } public SmtpPermissionAttribute(SecurityAction action) : base(action) { } public override IPermission CreatePermission() { return null; } } }