Thanks, Ned.  After taking a look at the library documentation, I decided to change the docstring in a somewhat different way.  In general in our docs we do not document all the possible exceptions a library can raise, but just the library-specific exceptions and the interesting special cases.  So what I did was to remove the language that implied that *only* SMTPExceptions were raised.  And then in the 3.4 docs noted that it is a subclass of IOError.