diff --git a/nixos/doc/manual/release-notes/rl-2105.xml b/nixos/doc/manual/release-notes/rl-2105.xml
index 302a6d3f3749..6868cea4a77c 100644
--- a/nixos/doc/manual/release-notes/rl-2105.xml
+++ b/nixos/doc/manual/release-notes/rl-2105.xml
@@ -523,6 +523,13 @@ self: super:
       as an hardware RNG, as it will automatically run the krngd task to periodically collect random
       data from the device and mix it into the kernel's RNG.
     </para>
+    <para>
+      The default SMTP port for GitLab has been changed to
+      <literal>25</literal> from its previous default of
+      <literal>465</literal>. If you depended on this default, you
+      should now set the <xref linkend="opt-services.gitlab.smtp.port" />
+      option.
+    </para>
    </listitem>
   </itemizedlist>
  </section>
diff --git a/nixos/modules/services/misc/gitlab.nix b/nixos/modules/services/misc/gitlab.nix
index 91a6cd90064c..0f01e36e6912 100644
--- a/nixos/modules/services/misc/gitlab.nix
+++ b/nixos/modules/services/misc/gitlab.nix
@@ -424,7 +424,7 @@ in {
 
         port = mkOption {
           type = types.int;
-          default = 465;
+          default = 25;
           description = "Port of the SMTP server for Gitlab.";
         };
 
@@ -684,7 +684,7 @@ in {
     };
 
     # Use postfix to send out mails.
-    services.postfix.enable = mkDefault true;
+    services.postfix.enable = mkDefault (cfg.smtp.enable && cfg.smtp.address == "localhost");
 
     users.users.${cfg.user} =
       { group = cfg.group;