typo...

Doc/lib/libmailbox.tex

@@ -107,7 +107,7 @@ have one externally visible method:
 \begin{methoddesc}[mailbox]{next}{}
 Return the next message in the mailbox, created with the optional
 \var{factory} argument passed into the mailbox object's constructor.
-By defaul this is an \class{rfc822.Message}
+By default this is an \class{rfc822.Message}
 object (see the \refmodule{rfc822} module).  Depending on the mailbox
 implementation the \var{fp} attribute of this object may be a true
 file object or a class instance simulating a file object, taking care