diff --git a/lib/net/imap/response_parser.rb b/lib/net/imap/response_parser.rb
index 2a73f2482..827e2ef94 100644
--- a/lib/net/imap/response_parser.rb
+++ b/lib/net/imap/response_parser.rb
@@ -978,10 +978,16 @@ def envelope
       #   env-bcc         = "(" 1*address ")" / nil
       def nlist__address
         return if NIL?
-        lpar; list = [address]; list << address until rpar?
+        lpar; list = [address]; list << address until (quirky_SP?; rpar?)
         list
       end
 
+      # Used when servers erroneously send an extra SP.
+      #
+      # As of 2023-11-28, Outlook.com (still) sends SP
+      #   between +address+ in <tt>env-*</tt> lists.
+      alias quirky_SP? SP?
+
       alias env_from     nlist__address
       alias env_sender   nlist__address
       alias env_reply_to nlist__address
diff --git a/test/net/imap/fixtures/response_parser/quirky_behaviors.yml b/test/net/imap/fixtures/response_parser/quirky_behaviors.yml
index 45bc3d19d..ef3b18a33 100644
--- a/test/net/imap/fixtures/response_parser/quirky_behaviors.yml
+++ b/test/net/imap/fixtures/response_parser/quirky_behaviors.yml
@@ -31,3 +31,11 @@
         unparsed_data: "froopy snood"
       raw_data: "* 86 NOOP froopy snood\r\n"
 
+  outlook.com puts an extra SP in ENVELOPE address lists:
+    comment: |
+      An annoying bug from outlook.com.  They've had the bug for years, and
+      still have the bug as of 2023-11-28.
+
+      The example comes from a real response, but all addesses have been
+      replaced by the `faker` gem. :)
+    :response: "* 24 FETCH (UID 60 INTERNALDATE \"24-May-2021 11:47:51 +0200\" RFC822.SIZE 49051 ENVELOPE (\"Mon, 24 May 20 21 09:47:50 +0000\" \"Zoooom Zoom\" ((\"Augustina Gleason\" NIL \"augustina\" \"oberbrunner.test\")) NIL NIL ((\"risa@harvey-lemke.test\" NIL \"risa\" \"harvey-lemke.test\") (\"shella@kilback-renner.test\" NIL \"shella\" \"kilback-renner.test\") (\"jana.kiehn@bradtke-considine.example\" NIL \"jana.kiehn\" \"bradtke-considine.example\") (\"frank@hartmann.test\" NIL \"frank\" \"hartmann.test\") (\"numbers.ryan@satterfield.test\" NIL \"numbers.ryan\" \"satterfield.test\") (\"keneth_feeney@will-walter.test\" NIL \"keneth_feeney\" \"will-walter.test\")) NIL NIL NIL \"<aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@bbbbbbbbbbbbb.ccccccc.PROD.OUTLOOK.COM>\"))\r\n"