<PackageReference Include="System.Security.Permissions" Version="10.0.2" />

System.Net.Mail.SmtpPermission

Controls access to Simple Mail Transport Protocol (SMTP) servers.
namespace System.Net.Mail { public sealed class SmtpPermission : CodeAccessPermission, IUnrestrictedPermission { public SmtpAccess Access { get; } public SmtpPermission(bool unrestricted); public SmtpPermission(SmtpAccess access); public SmtpPermission(PermissionState state); public void AddPermission(SmtpAccess access); public bool IsUnrestricted(); } }