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
@@ -1,428 +1,495 @@
 /*  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] =
+    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)
+
   sealed case class Message(
     name: String,
     date: Date,
     title: String,
     author_name: String,
     author_address: 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))
+    }
+
     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"
-
-    def normal_address: String = Word.lowercase(author_address)
-  }
+   }
 
   object Messages
   {
+    type Graph = isabelle.Graph[String, Message]
+
     def apply(msgs: List[Message]): Messages =
-      new Messages(msgs.sortBy(_.date)(Date.Ordering))
+    {
+      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
+        else g.default_node(node, msg)
+
+      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
+          }))
+    }
 
     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])
+    {
+      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])
+  class Messages private(val sorted: List[Message], val graph: Messages.Graph)
   {
-    override def toString: String = "Messages(" + sorted.length + ")"
+    override def toString: String = "Messages(" + sorted.size + ")"
 
-    def check(): Unit =
+    object Node_Ordering extends scala.math.Ordering[String]
     {
-      val proper = sorted.filter(msg => msg.author_name.nonEmpty && msg.author_address.nonEmpty)
-      val address_name = Multi_Map.from(proper.map(msg => (msg.normal_address, msg.author_name)))
-      val name_address = Multi_Map.from(proper.map(msg => (msg.author_name, msg.normal_address)))
+      override def compare(a: String, b: String): Int =
+        Date.Rev_Ordering.compare(graph.get_node(a).date, graph.get_node(b).date)
+    }
 
-      def print_dup(a: String, bs: List[String]): String =
-        "  * " + a + bs.mkString("\n      ", "\n      ", "")
+    def get_nodes(msg: Message): List[String] =
+      graph.all_succs(msg.nodes).sorted(Node_Ordering)
 
-      def print_dups(title: String, m: Multi_Map[String, String]): Unit =
-      {
-        val dups = m.iterator_list.filter(p => p._2.length > 1).toList
-        if (dups.nonEmpty) {
-          Output.writeln(cat_lines(title :: dups.map(p => print_dup(p._1, p._2))))
-        }
+    def get_cluster(msg: Message): Messages.Cluster =
+    {
+      val (addresses, names) = get_nodes(msg).partition(is_address)
+      Messages.Cluster(names, addresses)
+    }
+
+    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)))
       }
 
-      print_dups("\nduplicate names:", address_name)
-      print_dups("\nduplicate addresses:", name_address)
-
-      def get_name(msg: Message): Option[String] =
-        proper_string(msg.author_name) orElse address_name.get(msg.author_address)
-
-      val missing_name =
-        sorted.flatMap(msg =>
-          if (get_name(msg).isEmpty) Some(proper_string(msg.author_address).getOrElse(msg.name))
-          else None).toSet.toList.sorted
-
-      val missing_address =
-        sorted.flatMap(msg =>
-          if (msg.author_address.isEmpty) Some(proper_string(msg.author_name).getOrElse(msg.name))
-          else None).toSet.toList.sorted
-
-      if (missing_name.nonEmpty) {
-        Output.writeln(("missing name:" :: missing_name).mkString("\n", "\n  ", ""))
-      }
-
-      if (missing_address.nonEmpty) {
-        Output.writeln(("missing address:" :: missing_address).mkString("\n", "\n  ", ""))
+      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 =
-      str.replaceAll("""\s+""", " ").replaceAll(" at ", "@")
+    {
+      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))
+      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)] =
         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
         }
     }
 
     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) =
         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 tags = List(list_name)
 
-      Message(name, date, title, author_name, author_address, body, tags)
+      Message(name, date, title, standard_name(author_name), author_address, 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))
+      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 tags = List(list_name)
 
-      Message(name, date, title, author_name, author_address, body, tags)
+      Message(name, date, title, standard_name(author_name), author_address, body, tags)
     }
   }
 }