Add documentation for FTP.prefer_epsv attribute

Author: simonepelosi

Doc/library/ftplib.rst

@@ -276,6 +276,22 @@ FTP objects
       prints the line to :data:`sys.stdout`.
 
 
+   .. attribute:: FTP.prefer_epsv
+
+      A :class:`bool` that controls whether :meth:`makepasv` tries the EPSV
+      command (RFC 2428) before falling back to PASV on IPv4 connections.
+      Defaults to ``True``.
+
+      EPSV responses contain only a port number and no IP address, making them
+      transparent to firewall FTP Application Layer Gateways (ALGs) that
+      commonly intercept and mangle PASV responses.  If the server does not
+      support EPSV, :meth:`makepasv` falls back to PASV automatically.
+
+      Set to ``False`` to restore the legacy PASV-first behavior on IPv4.
+
+      .. versionadded:: 3.15
+
+
    .. method:: FTP.set_pasv(val)
 
       Enable "passive" mode if *val* is true, otherwise disable passive mode.

Misc/NEWS.d/next/Library/2026-05-22-12-00-00.gh-issue-127478.EpsvFtp.rst

@@ -1,4 +1,4 @@
-:mod:`ftplib`: :meth:`~ftplib.FTP.makepasv` now prefers EPSV (RFC 2428) over
+:mod:`ftplib`: Passive mode data connections now prefer EPSV (RFC 2428) over
 PASV on IPv4 connections, falling back to PASV if the server does not support
 EPSV. EPSV is firewall-transparent as it does not embed an IP address in the
 response, avoiding interference from firewall FTP Application Layer Gateways