added mail module;

--- a/etc/build.props	Thu Oct 26 11:29:00 2023 +0200
+++ b/etc/build.props	Tue Oct 24 19:17:46 2023 +0200
@@ -87,6 +87,7 @@
   src/Pure/General/linear_set.scala \
   src/Pure/General/logger.scala \
   src/Pure/General/long_name.scala \
+  src/Pure/General/mail.scala \
   src/Pure/General/mailman.scala \
   src/Pure/General/mercurial.scala \
   src/Pure/General/multi_map.scala \

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/General/mail.scala	Tue Oct 24 19:17:46 2023 +0200
@@ -0,0 +1,109 @@
+/*  Title:      Pure/General/mail.scala
+    Author:     Fabian Huch, TU Muenchen
+
+Support for sending text mails via SMTP.
+*/
+
+package isabelle
+
+
+import java.util.Properties as JProperties
+import javax.mail.internet.{InternetAddress, MimeMessage}
+import javax.mail.{AuthenticationFailedException, Authenticator, Message, MessagingException, PasswordAuthentication, Transport as JTransport, Session as JSession}
+
+
+object Mail {
+  /* validated addresses */
+
+  final class Address private[Mail](rep: String) {
+    override def toString: String = rep
+  }
+
+  val default_address: Address = address("user@localhost")
+  def address(s: String): Address =
+    Exn.capture(new InternetAddress(s).validate()) match {
+      case Exn.Res(_) => new Address(s)
+      case _ => error("Invalid mail address: " + quote(s))
+    }
+
+
+  /* smtp server */
+
+  enum Transport {
+    case Plaintext extends Transport
+    case SSL(protocol: String = "TLSv1.2") extends Transport
+    case STARTTLS extends Transport
+  }
+
+  class Server (
+    sender: Address,
+    smtp_host: String,
+    smtp_port: Int = 587,
+    user: String = "",
+    password: String = "",
+    transport: Transport = Transport.SSL()
+  ) {
+    def use_auth: Boolean = user.nonEmpty && password.nonEmpty
+
+    private def mail_session: JSession = {
+      val props = new JProperties()
+      props.setProperty("mail.smtp.host", smtp_host)
+      props.setProperty("mail.smtp.port", smtp_port.toString)
+      props.setProperty("mail.smtp.auth", use_auth.toString)
+
+      transport match {
+        case Transport.SSL(protocol) =>
+          props.setProperty("mail.smtp.ssl.enable", "true")
+         props.setProperty("mail.smtp.ssl.protocols", protocol)
+        case Transport.STARTTLS =>
+          props.setProperty("mail.smtp.starttls.enable", "true")
+        case Transport.Plaintext =>
+      }
+
+      val authenticator = new Authenticator() {
+        override def getPasswordAuthentication = new PasswordAuthentication(user, password)
+      }
+      JSession.getDefaultInstance(props, authenticator)
+    }
+
+    def defined: Boolean = smtp_host.nonEmpty
+    def check(): Unit = {
+      val transport = mail_session.getTransport("smtp")
+      try {
+        transport.connect(smtp_host, smtp_port, user, password)
+        transport.close()
+      }
+      catch {
+        case exn: Throwable => error("Could not connect to SMTP server: " + exn.getMessage)
+      }
+    }
+
+    def send(mail: Mail): Unit = {
+      val from_address = mail.from_address.getOrElse(sender)
+      val from =
+        if (mail.from_name.isEmpty) new InternetAddress(from_address.toString)
+        else new InternetAddress(from_address.toString, mail.from_name)
+
+      val message = new MimeMessage(mail_session)
+      message.setFrom(from)
+      message.setSender(new InternetAddress(sender.toString))
+      message.setSubject(mail.subject)
+      message.setText(mail.content, "UTF-8")
+      message.setSentDate(new java.util.Date())
+
+      for (recipient <- mail.recipients) {
+        message.addRecipient(Message.RecipientType.TO, new InternetAddress(recipient.toString))
+      }
+
+      try { JTransport.send(message) }
+      catch { case exn: Throwable => error("Sending mail failed: " + exn.getMessage) }
+    }
+  }
+}
+
+case class Mail(
+  subject: String,
+  recipients: List[Mail.Address],
+  content: String,
+  from_address: Option[Mail.Address] = None,
+  from_name: String = "")