diff --git a/src/Pure/General/mailman.scala b/src/Pure/General/mailman.scala
--- a/src/Pure/General/mailman.scala
+++ b/src/Pure/General/mailman.scala
@@ -1,495 +1,483 @@
 /*  Title:      Pure/General/mailman.scala
     Author:     Makarius
 
 Support for Mailman list servers.
 */
 
 package isabelle
 
 
 import java.net.URL
 
 import scala.annotation.tailrec
 import scala.util.matching.Regex
 import scala.util.matching.Regex.Match
 
 
 object Mailman
 {
   /* mailing list messages */
 
   def is_address(s: String): Boolean =
     s.contains('@') && s.contains('.') && !s.contains(' ')
 
-  val standard_name: Map[String, String] =
+  private val standard_name: Map[String, String] =
     Map(
       "Blanchette, J.C." -> "Jasmin Christian Blanchette",
       "Buday Gergely István" -> "Gergely Buday",
       "Carsten Schuermann" -> "Carsten Schürman",
       "Christoph Lueth" -> "Christoph Lüth",
       "Claude Marche" -> "Claude Marché",
       "Farquhar, Colin I" -> "Colin Farquhar",
       "George K." -> "George Karabotsos",
       "Filip MariÄ" -> "Filip Marić",
       "Hitoshi Ohsaki (RTA publicity chair)" -> "Hitoshi Ohsaki",
       "Farn" -> "Farn Wang",
       "Fleury Mathias" -> "Mathias Fleury",
       "Urban, Christian" -> "Christian Urban",
       "Moscato, Mariano M. \\(LARC-D320\\)\\[NATIONAL INSTITUTE OF AEROSPACE\\]" -> "Moscato, Mariano M. (LARC-D320)",
     ).withDefault(identity)
 
+  def standard_author_info(author_info: List[String]): List[String] =
+    author_info.map(standard_name).filter(_.nonEmpty).distinct
+
   sealed case class Message(
     name: String,
     date: Date,
     title: String,
-    author_name: String,
-    author_address: String,
+    author_info: List[String],
     body: String,
     tags: List[String])
   {
-    if (author_name.nonEmpty && is_address(author_name)) {
-      Output.warning("Bad author name, looks like mail address: " +
-        quote(author_name) + " in " + quote(name))
-    }
-
-    if (author_address.nonEmpty && !is_address(author_address)) {
-      error("Bad mail address: " + quote(author_address) + " in " + quote(name))
+    if (author_info.isEmpty || author_info.exists(_.isEmpty)) {
+      error("Bad author information in " + quote(name))
     }
 
     override def toString: String = name
-
-    def nodes: List[String] =
-      proper_string(author_name).toList :::
-      proper_string(author_address).toList
-
-    def print: String =
-      name + "\n" + date + "\n" + title + "\n" +
-      quote(author_name) + "\n" + "<" + author_address + ">\n"
    }
 
   object Messages
   {
     type Graph = isabelle.Graph[String, Message]
 
     def apply(msgs: List[Message]): Messages =
     {
-      def update_node(g: Graph, node: String, msg: Message): Graph =
-        if (node.isEmpty ||
-            g.defined(node) && Date.Ordering.compare(g.get_node(node).date, msg.date) >= 0) g
+      def make_node(g: Graph, node: String, msg: Message): Graph =
+        if (g.defined(node) && Date.Ordering.compare(g.get_node(node).date, msg.date) >= 0) g
         else g.default_node(node, msg)
 
+      def connect_nodes(g: Graph, nodes: List[String]): Graph =
+        nodes match {
+          case Nil => g
+          case a :: bs => bs.foldLeft(g)({ case (g1, b) => g1.add_edge(a, b).add_edge(b, a) })
+        }
+
       new Messages(msgs.sortBy(_.date)(Date.Ordering),
         msgs.foldLeft[Graph](Graph.string)(
-          { case (g, msg) =>
-              val a = msg.author_name
-              val b = msg.author_address
-              val g1 = update_node(update_node(g, a, msg), b, msg)
-              if (a.nonEmpty && b.nonEmpty) g1.add_edge(a, b).add_edge(b, a)
-              else g1
+          { case (graph, msg) =>
+              val nodes = msg.author_info
+              connect_nodes(nodes.foldLeft(graph)(make_node(_, _, msg)), nodes)
           }))
     }
 
     def find(dir: Path): Messages =
     {
       val msgs =
         for {
           archive <- List(Isabelle_Users, Isabelle_Dev)
           msg <- archive.find_messages(dir + Path.basic(archive.list_name))
         } yield msg
       Messages(msgs)
     }
 
-    sealed case class Cluster(names: List[String], addresses: List[String])
+    sealed case class Cluster(author_info: List[String])
     {
+      val (addresses, names) = author_info.partition(is_address)
+
       val name: String =
         names.headOption getOrElse {
           addresses match {
             case a :: _ => a.substring(0, a.indexOf('@')).replace('.', ' ')
             case Nil => error("Empty cluster")
           }
         }
 
       def get_address: Option[String] = addresses.headOption
 
       def unique: Boolean = names.length == 1 && addresses.length == 1
       def multi: Boolean = names.length > 1 || addresses.length > 1
 
       def print: String =
       {
         val entries = names ::: (if (addresses.isEmpty) Nil else List("")) ::: addresses
         entries.mkString("\n  * ", "\n    ", "")
       }
     }
   }
 
   class Messages private(val sorted: List[Message], val graph: Messages.Graph)
   {
     override def toString: String = "Messages(" + sorted.size + ")"
 
     object Node_Ordering extends scala.math.Ordering[String]
     {
       override def compare(a: String, b: String): Int =
         Date.Rev_Ordering.compare(graph.get_node(a).date, graph.get_node(b).date)
     }
 
-    def get_nodes(msg: Message): List[String] =
-      graph.all_succs(msg.nodes).sorted(Node_Ordering)
-
     def get_cluster(msg: Message): Messages.Cluster =
-    {
-      val (addresses, names) = get_nodes(msg).partition(is_address)
-      Messages.Cluster(names, addresses)
-    }
+      Messages.Cluster(graph.all_succs(msg.author_info).sorted.sorted(Node_Ordering))
 
     def get_name(msg: Message): String = get_cluster(msg).name
 
     def get_address(msg: Message): String =
       get_cluster(msg).get_address getOrElse error("No author address for " + quote(msg.name))
 
     def check(check_multi: Boolean = false): Unit =
     {
       val clusters = sorted.map(get_cluster).distinct.sortBy(_.name)
 
       val multi = if (check_multi) clusters.filter(_.multi) else Nil
       if (multi.nonEmpty) {
         Output.writeln(cat_lines("ambiguous:" :: multi.map(_.print)))
       }
 
       val unknown = clusters.filter(cluster => cluster.get_address.isEmpty)
       if (unknown.nonEmpty) {
         Output.writeln(cat_lines("unknown mail:" :: unknown.map(_.print)))
       }
     }
   }
 
 
   /* mailing list archives */
 
   abstract class Archive(
     url: URL,
     name: String = "",
     tag: String = "")
   {
     def message_regex: Regex
     def message_content(name: String, lines: List[String]): Message
 
     def message_match(lines: List[String], re: Regex): Option[Match] =
       lines.flatMap(re.findFirstMatchIn(_)).headOption
 
     def make_name(str: String): String =
     {
       val s = str.trim.replaceAll("""\s+""", " ").replaceAll(" at ", "@")
       if (s.startsWith("=") && s.endsWith("=")) "" else s
     }
 
     def make_body(lines: List[String]): String =
       cat_lines(Library.take_suffix[String](_.isEmpty, lines)._1)
 
     private val main_url: URL =
       Url(Library.take_suffix[Char](_ == '/', Url.trim_index(url).toString.toList)._1.mkString + "/")
 
     private val main_html = Url.read(main_url)
 
     val list_name: String =
     {
       val title =
         """<title>The ([^</>]*) Archives</title>""".r.findFirstMatchIn(main_html).map(_.group(1))
       (proper_string(name) orElse title).getOrElse(error("Failed to determine mailing list name"))
     }
     override def toString: String = list_name
 
     def full_name(href: String): String = list_name + "/" + href
 
     def list_tag: String = proper_string(tag).getOrElse(list_name)
 
     def read_text(href: String): String = Url.read(new URL(main_url, href))
 
     def hrefs_text: List[String] =
       """href="([^"]+\.txt(?:\.gz)?)"""".r.findAllMatchIn(main_html).map(_.group(1)).toList
 
     def hrefs_msg: List[String] =
       (for {
         href <- """href="([^"]+)/date.html"""".r.findAllMatchIn(main_html).map(_.group(1))
         html = read_text(href + "/date.html")
         msg <- message_regex.findAllMatchIn(html).map(_.group(1))
       } yield href + "/" + msg).toList
 
     def get(target_dir: Path, href: String, progress: Progress = new Progress): Option[Path] =
     {
       val dir = target_dir + Path.basic(list_name)
       val path = dir + Path.explode(href)
       val url = new URL(main_url, href)
       val connection = url.openConnection
       try {
         val length = connection.getContentLengthLong
         val timestamp = connection.getLastModified
         val file = path.file
         if (file.isFile && file.length == length && file.lastModified == timestamp) None
         else {
           Isabelle_System.make_directory(path.dir)
           progress.echo("Getting " + url)
           val bytes =
             using(connection.getInputStream)(Bytes.read_stream(_, hint = length.toInt max 1024))
           Bytes.write(file, bytes)
           file.setLastModified(timestamp)
           Some(path)
         }
       }
       finally { connection.getInputStream.close() }
     }
 
     def download_text(target_dir: Path, progress: Progress = new Progress): List[Path] =
       hrefs_text.flatMap(get(target_dir, _, progress = progress))
 
     def download_msg(target_dir: Path, progress: Progress = new Progress): List[Path] =
       hrefs_msg.flatMap(get(target_dir, _, progress = progress))
 
     def download(target_dir: Path, progress: Progress = new Progress): List[Path] =
       download_text(target_dir, progress = progress) :::
       download_msg(target_dir, progress = progress)
 
     def make_title(str: String): String =
     {
       val Trim1 = ("""\s*\Q[""" + list_tag + """]\E\s*(.*)""").r
       val Trim2 = """(?i:(?:re|fw|fwd)\s*:\s*)(.*)""".r
       val Trim3 = """\[\s*(.*?)\s*\]""".r
       @tailrec def trim(s: String): String =
         s match {
           case Trim1(s1) => trim(s1)
           case Trim2(s1) => trim(s1)
           case Trim3(s1) => trim(s1)
           case _ => s
         }
       trim(str)
     }
 
     def get_messages(): List[Message] =
       for (href <- hrefs_msg) yield message_content(href, split_lines(read_text(href)))
 
     def find_messages(dir: Path): List[Message] =
     {
       for {
         file <- File.find_files(dir.file, file => file.getName.endsWith(".html"))
         rel_path <- File.relative_path(dir, File.path(file))
       }
       yield {
         val name = full_name(rel_path.implode)
         message_content(name, split_lines(File.read(file)))
       }
     }
   }
 
   private class Message_Chunk(bg: String = "", en: String = "")
   {
     def unapply(lines: List[String]): Option[List[String]] =
     {
       val res1 =
         if (bg.isEmpty) Some(lines)
         else {
           lines.dropWhile(_ != bg) match {
             case Nil => None
             case _ :: rest => Some(rest)
           }
         }
       if (en.isEmpty) res1
       else {
         res1 match {
           case None => None
           case Some(lines1) =>
             val lines2 = lines1.takeWhile(_ != en)
             if (lines1.drop(lines2.length).isEmpty) None else Some(lines2)
         }
       }
     }
 
     def get(lines: List[String]): List[String] =
       unapply(lines) getOrElse
         error("Missing delimiters:" +
           (if (bg.nonEmpty) " " else "") + bg +
           (if (en.nonEmpty) " " else "") + en)
   }
 
 
   /* isabelle-users mailing list */
 
   object Isabelle_Users extends Archive(
     Url("https://lists.cam.ac.uk/pipermail/cl-isabelle-users"),
     name = "isabelle-users", tag = "isabelle")
   {
     override def message_regex: Regex = """<li><a name="\d+" href="(msg\d+\.html)">""".r
 
     private object Head extends
       Message_Chunk(bg = "<!--X-Head-of-Message-->", en = "<!--X-Head-of-Message-End-->")
 
     private object Body extends
       Message_Chunk(bg = "<!--X-Body-of-Message-->", en = "<!--X-Body-of-Message-End-->")
 
     private object Date_Format
     {
       private val Trim1 = """\w+,\s*(.*)""".r
       private val Trim2 = """(.*?)\s*\(.*\)""".r
       private val Format =
         Date.Format(
           "d MMM uuuu H:m:s Z",
           "d MMM uuuu H:m:s z",
           "d MMM yy H:m:s Z",
           "d MMM yy H:m:s z")
       def unapply(s: String): Option[Date] =
       {
         val s0 = s.replaceAll("""\s+""", " ")
         val s1 =
           s0 match {
             case Trim1(s1) => s1
             case _ => s0
           }
         val s2 =
           s1 match {
             case Trim2(s2) => s2
             case _ => s1
           }
         Format.unapply(s2)
       }
     }
 
     override def make_name(str: String): String =
     {
       val s = Library.perhaps_unsuffix(" via Cl-isabelle-users", super.make_name(str))
       if (s == "cl-isabelle-users@lists.cam.ac.uk") "" else s
     }
 
     object Address
     {
       private def anchor(s: String): String = """<a href="[^"]*">""" + s + """</a>"""
       private def angl(s: String): String = """&lt;""" + s + """&gt;"""
       private def quot(s: String): String = """&quot;""" + s + """&quot;"""
       private def paren(s: String): String = """\(""" + s + """\)"""
       private val adr = """([^<>]*? at [^<>]*?)"""
       private val any = """([^<>]*?)"""
       private val spc = """\s*"""
 
       private val Name1 = quot(anchor(any)).r
       private val Name2 = quot(any).r
       private val Name_Adr1 = (quot(anchor(any)) + spc + angl(anchor(adr))).r
       private val Name_Adr2 = (quot(any) + spc + angl(anchor(adr))).r
       private val Name_Adr3 = (anchor(any) + spc + angl(anchor(adr))).r
       private val Name_Adr4 = (any + spc + angl(anchor(adr))).r
       private val Adr_Name1 = (angl(anchor(adr)) + spc + paren(any)).r
       private val Adr_Name2 = (anchor(adr) + spc + paren(any)).r
       private val Adr1 = angl(anchor(adr)).r
       private val Adr2 = anchor(adr).r
 
-      def unapply(s: String): Option[(String, String)] =
+      def parse(s: String): List[String] =
         s match {
-          case Name1(a) => Some((make_name(a), ""))
-          case Name2(a) => Some((make_name(a), ""))
-          case Name_Adr1(a, b) => Some((make_name(a), make_name(b)))
-          case Name_Adr2(a, b) => Some((make_name(a), make_name(b)))
-          case Name_Adr3(a, b) => Some((make_name(a), make_name(b)))
-          case Name_Adr4(a, b) => Some((make_name(a), make_name(b)))
-          case Adr_Name1(b, a) => Some((make_name(a), make_name(b)))
-          case Adr_Name2(b, a) => Some((make_name(a), make_name(b)))
-          case Adr1(a) => Some(("", make_name(a)))
-          case Adr2(a) => Some(("", make_name(a)))
-          case _ => None
+          case Name1(a) => List(a)
+          case Name2(a) => List(a)
+          case Name_Adr1(a, b) => List(a, b)
+          case Name_Adr2(a, b) => List(a, b)
+          case Name_Adr3(a, b) => List(a, b)
+          case Name_Adr4(a, b) => List(a, b)
+          case Adr_Name1(b, a) => List(a, b)
+          case Adr_Name2(b, a) => List(a, b)
+          case Adr1(a) => List(a)
+          case Adr2(a) => List(a)
+          case _ => Nil
         }
     }
 
     override def message_content(name: String, lines: List[String]): Message =
     {
       def err(msg: String = ""): Nothing =
         error("Malformed message: " + name + (if (msg.isEmpty) "" else "\n" + msg))
 
       val (head, body) =
         try { (Head.get(lines), make_body(Body.get(lines))) }
         catch { case ERROR(msg) => err(msg) }
 
       val date =
         message_match(head, """<li><em>Date</em>:\s*(.*?)\s*</li>""".r)
           .map(m => HTML.input(m.group(1))) match
         {
           case Some(Date_Format(d)) => d
           case Some(s) => err("Malformed Date: " + quote(s))
           case None => err("Missing Date")
         }
 
       val title =
         make_title(
           HTML.input(message_match(head, """<li><em>Subject</em>:\s*(.*)</li>""".r)
             .getOrElse(err("Missing Subject")).group(1)))
 
-      val (author_name, author_address) =
+      val author_info =
         message_match(head, """<li><em>From</em>:\s*(.*?)\s*</li>""".r) match {
           case None => err("Missing From")
           case Some(m) =>
-            val (a0, b0) = Address.unapply(m.group(1)) getOrElse err("Malformed From")
-            val a = HTML.input(a0)
-            val b = HTML.input(b0)
-            (if (a == b) "" else a, b)
+            val res =
+              Address.parse(m.group(1)).map(a => HTML.input(make_name(a)))
+                .distinct.filter(_.nonEmpty)
+            if (res.nonEmpty) res else err("Malformed author information")
         }
 
       val tags = List(list_name)
 
-      Message(name, date, title, standard_name(author_name), author_address, body, tags)
+      Message(name, date, title, standard_author_info(author_info), body, tags)
     }
   }
 
 
   /* isabelle-dev mailing list */
 
   object Isabelle_Dev extends Archive(Url("https://mailmanbroy.in.tum.de/pipermail/isabelle-dev"))
   {
     override def message_regex: Regex = """<LI><A HREF="(\d+\.html)">""".r
 
     private object Head extends Message_Chunk(en = "<!--beginarticle-->")
     private object Body extends Message_Chunk(bg = "<!--beginarticle-->", en = "<!--endarticle-->")
 
     private object Date_Format
     {
       val Format = Date.Format("E MMM d H:m:s z uuuu")
       def unapply(s: String): Option[Date] = Format.unapply(s.replaceAll("""\s+""", " "))
     }
 
     override def make_name(str: String): String =
     {
       val s = Library.perhaps_unsuffix(" via RT", super.make_name(str))
       if (s == "sys-admin@cl.cam.ac.uk") "" else s
     }
 
     override def message_content(name: String, lines: List[String]): Message =
     {
       def err(msg: String = ""): Nothing =
         error("Malformed message: " + name + (if (msg.isEmpty) "" else "\n" + msg))
 
       val (head, body) =
         try { (Head.get(lines), make_body(Body.get(lines))) }
         catch { case ERROR(msg) => err(msg) }
 
       val date =
         message_match(head, """\s*<I>(.*)</I>""".r).map(m => HTML.input(m.group(1))) match {
           case Some(Date_Format(d)) => d
           case Some(s) => err("Malformed Date: " + quote(s))
           case None => err("Missing Date")
         }
 
       val (title, author_address) =
       {
         message_match(head, """TITLE="([^"]+)">(.*)""".r) match {
           case Some(m) => (make_title(HTML.input(m.group(1))), make_name(HTML.input(m.group(2))))
           case None => err("Missing TITLE")
         }
       }
 
       val author_name =
         message_match(head, """\s*<B>(.*)</B>""".r) match {
           case None => err("Missing author")
           case Some(m) =>
             val a = make_name(HTML.input(m.group(1)))
             if (a == author_address) "" else a
         }
 
+      val author_info = List(author_name, author_address)
       val tags = List(list_name)
 
-      Message(name, date, title, standard_name(author_name), author_address, body, tags)
+      Message(name, date, title, standard_author_info(author_info), body, tags)
     }
   }
 }