diff --git a/management/daemon.py b/management/daemon.py
index 695b2a1..69bb929 100755
--- a/management/daemon.py
+++ b/management/daemon.py
@@ -98,7 +98,7 @@ def me():
 @authorized_personnel_only
 def mail_users():
 	if request.args.get("format", "") == "json":
-		return json_response(get_mail_users_ex(env, with_archived=True))
+		return json_response(get_mail_users_ex(env, with_archived=True, with_slow_info=True))
 	else:
 		return "".join(x+"\n" for x in get_mail_users(env))
 
diff --git a/management/mailconfig.py b/management/mailconfig.py
index 74b3c71..603934d 100755
--- a/management/mailconfig.py
+++ b/management/mailconfig.py
@@ -53,7 +53,7 @@ def get_mail_users(env):
 	users = [ row[0] for row in c.fetchall() ]
 	return utils.sort_email_addresses(users, env)
 
-def get_mail_users_ex(env, with_archived=False):
+def get_mail_users_ex(env, with_archived=False, with_slow_info=False):
 	# Returns a complex data structure of all user accounts, optionally
 	# including archived (status="inactive") accounts.
 	#
@@ -86,15 +86,20 @@ def get_mail_users_ex(env, with_archived=False):
 	c.execute('SELECT email, privileges FROM users')
 	for email, privileges in c.fetchall():
 		active_accounts.add(email)
-		users.append({
+
+		user = {
 			"email": email,
 			"privileges": parse_privs(privileges),
 			"status": "active",
-			"aliases": [
+		}
+		users.append(user)
+
+		if with_slow_info:
+			user["aliases"] = [
 				(alias, sorted(evaluate_mail_alias_map(alias, aliases, env)))
 				for alias in aliases.get(email.lower(), [])
 				]
-		})
+			user["mailbox_size"] = utils.du(os.path.join(env['STORAGE_ROOT'], 'mail/mailboxes', *reversed(email.split("@"))))
 
 	# Add in archived accounts.
 	if with_archived:
@@ -102,13 +107,17 @@ def get_mail_users_ex(env, with_archived=False):
 		for domain in os.listdir(root):
 			for user in os.listdir(os.path.join(root, domain)):
 				email = user + "@" + domain
+				mbox = os.path.join(root, domain, user)
 				if email in active_accounts: continue
-				users.append({
+				user = {
 					"email": email, 
 					"privileges": "",
 					"status": "inactive",
-					"mailbox": os.path.join(root, domain, user),
-				})
+					"mailbox": mbox,
+				}
+				users.append(user)
+				if with_slow_info:
+					user["mailbox_size"] = utils.du(mbox)
 
 	# Group by domain.
 	domains = { }
diff --git a/management/templates/system-backup.html b/management/templates/system-backup.html
index 8f01243..2b1ad46 100644
--- a/management/templates/system-backup.html
+++ b/management/templates/system-backup.html
@@ -39,7 +39,12 @@ function nice_size(bytes) {
     bytes /= 1024;
     powers.shift();
   }
-  return (Math.round(bytes*10)/10) + " " + powers[0];
+  // round to have three significant figures but at most one decimal place
+  if (bytes >= 100)
+    bytes = Math.round(bytes)
+  else
+    bytes = Math.round(bytes*10)/10;
+  return bytes + " " + powers[0];
 }
 
 function show_system_backup() {
diff --git a/management/templates/users.html b/management/templates/users.html
index 8b07af6..3f54cac 100644
--- a/management/templates/users.html
+++ b/management/templates/users.html
@@ -1,8 +1,8 @@
 <h2>Users</h2>
 
 <style>
-#user_table tr.account_inactive td .address { color: #888; text-decoration: line-through; }
-#user_table .aliases { margin-top: .33em; font-size: 95%; }
+#user_table tr.account_inactive td.address { color: #888; text-decoration: line-through; }
+#user_table .aliases { font-size: 90%; }
 #user_table .aliases div:before { content: "⇖ "; }
 #user_table .aliases div {  }
 #user_table .actions { margin-top: .33em; font-size: 95%; }
@@ -38,6 +38,13 @@
 
 <h3>Existing mail users</h3>
 <table id="user_table" class="table" style="width: auto">
+  <thead>
+    <tr>
+      <th width="50%">Email Address</th>
+      <th>Actions</th>
+      <th>Mailbox Size</th>
+    </tr>
+  </thead>
   <tbody>
   </tbody>
 </table>
@@ -45,10 +52,9 @@
 <div style="display: none">
   <table>
   <tr id="user-template">
-    <td class='email'>
-      <div class='address'> </div>
-
-      <div class='actions'>
+    <td class='address'>
+    </td>
+    <td class='actions'>
         <span class='privs'>
         </span>
 
@@ -65,9 +71,13 @@
         <a href="#" onclick="users_remove(this); return false;" class='if_active' title="Archive Account">
           archive account
         </a>
-
-        <div class='if_inactive restore_info' style='color: #888; font-size: 90%'>To restore account, create a new account with this email address. Or to permanently delete the mailbox, delete the directory <tt></tt> on the machine.</div>
-      </div>
+    </td>
+    <td class='mailboxsize'>
+    </td>
+  </tr>
+  <tr id="user-extra-template">
+    <td colspan="3" style="border-top: 0; padding-top: 0">
+      <div class='if_inactive restore_info' style='color: #888; font-size: 90%'>To restore account, create a new account with this email address. Or to permanently delete the mailbox, delete the directory <tt></tt> on the machine.</div>
 
       <div class='aliases' style='display: none'> </div>
     </td>
@@ -94,13 +104,19 @@ function show_users() {
           var user = r[i].users[k];
 
           var n = $("#user-template").clone();
+          var n2 = $("#user-extra-template").clone();
           n.attr('id', '');
+          n2.attr('id', '');
+          $('#user_table tbody').append(n);
+          $('#user_table tbody').append(n2);
 
           n.addClass("account_" + user.status);
+          n2.addClass("account_" + user.status);
+
           n.attr('data-email', user.email);
-          n.find('td.email .address').text(user.email)
-          $('#user_table tbody').append(n);
-          n.find('.restore_info tt').text(user.mailbox);
+          n.find('.address').text(user.email)
+          n.find('.mailboxsize').text(nice_size(user.mailbox_size))
+          n2.find('.restore_info tt').text(user.mailbox);
 
           if (user.status == 'inactive') continue;
 
@@ -121,9 +137,9 @@ function show_users() {
           }
 
           if (user.aliases && user.aliases.length > 0) {
-            n.find('.aliases').show();
+            n2.find('.aliases').show();
             for (var j = 0; j < user.aliases.length; j++) {
-              n.find('td.email .aliases').append($("<div/>").text(
+              n2.find('.aliases').append($("<div/>").text(
                 user.aliases[j][0]
                 + (user.aliases[j][1].length > 0 ? " ⇐ " + user.aliases[j][1].join(", ") : "")
                 ))
diff --git a/management/utils.py b/management/utils.py
index f7bc129..24a2a0a 100644
--- a/management/utils.py
+++ b/management/utils.py
@@ -165,3 +165,22 @@ def create_syslog_handler():
     handler = logging.handlers.SysLogHandler(address='/dev/log')
     handler.setLevel(logging.WARNING)
     return handler
+
+def du(path):
+    # Computes the size of all files in the path, like the `du` command.
+    # Based on http://stackoverflow.com/a/17936789. Takes into account
+    # soft and hard links.
+    total_size = 0
+    seen = set()
+    for dirpath, dirnames, filenames in os.walk(path):
+        for f in filenames:
+            fp = os.path.join(dirpath, f)
+            try:
+                stat = os.lstat(fp)
+            except OSError:
+                continue
+            if stat.st_ino in seen:
+                continue
+            seen.add(stat.st_ino)
+            total_size += stat.st_size
+    return total_size