Document smtp.SMTPAuthenticationError.
(backport from rev. 56129)
diff --git a/Doc/lib/libsmtplib.tex b/Doc/lib/libsmtplib.tex
index 3d74dd8..2e41373 100644
--- a/Doc/lib/libsmtplib.tex
+++ b/Doc/lib/libsmtplib.tex
@@ -74,6 +74,10 @@
The server refused our \samp{HELO} message.
\end{excdesc}
+\begin{excdesc}{SMTPAuthenticationError}
+ SMTP authentication went wrong. Most probably the server didn't accept
+ the username/password combination provided.
+\end{excdesc}
\begin{seealso}
\seerfc{821}{Simple Mail Transfer Protocol}{Protocol definition for