# HG changeset patch
# Parent 30a20f69a9194ff485f4273e152f13ce3246590f

diff --git a/Lib/mailbox.py b/Lib/mailbox.py
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -273,11 +273,9 @@
             else:
                 raise NoSuchMailboxError(self._path)
         self._toc = {}
-        self._toc_mtimes = {}
-        for subdir in ('cur', 'new'):
-            self._toc_mtimes[subdir] = os.path.getmtime(self._paths[subdir])
-        self._last_read = time.time()  # Records last time we read cur/new
-        self._skewfactor = 0.1         # Adjust if os/fs clocks are skewing
+        self._toc_mtimes = {'cur': 0, 'new': 0}
+        self._last_read = 0         # Records last time we read cur/new
+        self._skewfactor = 0.1      # Adjust if os/fs clocks are skewing
 
     def add(self, message):
         """Add message and return assigned key."""
@@ -520,15 +518,14 @@
         # extra delta to our wait.  The default is one tenth second, but is an
         # instance variable and so can be adjusted if dealing with a
         # particularly skewed or irregular system.
-        if time.time() - self._last_read > 2 + self._skewfactor:
-            refresh = False
-            for subdir in self._toc_mtimes:
-                mtime = os.path.getmtime(self._paths[subdir])
-                if mtime > self._toc_mtimes[subdir]:
-                    refresh = True
-                self._toc_mtimes[subdir] = mtime
-            if not refresh:
-                return
+        refresh = (time.time() < self._last_read + 2 + self._skewfactor)
+        for subdir in self._toc_mtimes:
+            mtime = os.path.getmtime(self._paths[subdir])
+            if mtime > self._toc_mtimes[subdir]:
+                refresh = True
+            self._toc_mtimes[subdir] = mtime
+        if not refresh:
+            return
         # Refresh toc
         self._toc = {}
         for subdir in self._toc_mtimes:
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -801,6 +801,25 @@
                                           key1: os.path.join('new', key1),
                                           key2: os.path.join('new', key2)})
 
+    def test_refresh_after_safety_period(self):
+        # Issue #13254: Call _refresh after the "file system safety
+        # period" of 2 seconds has passed; _toc should still be
+        # updated because this is the first call to _refresh.
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(self._template % 1)
+
+        self._box = self._factory(self._path)
+        self.assertEqual(self._box._toc, {})
+
+        # Emulate sleeping. Instead of sleeping for 2 seconds, use the
+        # skew factor to make _refresh think that the filesystem
+        # safety period has passed and re-reading the _toc is only
+        # required if mtimes differ.
+        self._box._skewfactor = -2
+
+        self._box._refresh()
+        self.assertEqual(sorted(self._box._toc.keys()), sorted([key0, key1]))
+
     def test_lookup(self):
         # Look up message subpaths in the TOC
         self.assertRaises(KeyError, lambda: self._box._lookup('foo'))
@@ -876,6 +895,8 @@
         self.assertFalse((perms & 0o111)) # Execute bits should all be off.
 
     def test_reread(self):
+        # Do an initial unconditional refresh
+        self._box._refresh()
 
         # Put the last modified times more than two seconds into the past
         # (because mtime may have a two second granularity)