The only comment I have is, if the caller needs to organise when to auth and instigate tls then for completeness getcapabilities() should have an option to force a reget of the current capabilities, in line with rfc3977 5.2.2:

> An NNTP client MAY cache the results of this command, but MUST NOT 
> rely on the correctness of any cached results, whether from earlier
> in this session or from a previous session, MUST cope gracefully 
> with the cached status being out of date, and SHOULD (if caching
> results) provide a way to force the cached information to be
> refreshed.

As it stands, the nntplib can cause the cached capabilities to be refreshed at certain points automatically (as it should), but I 
think it should be possible for the caller of the method to also specify that fresh capabilities are required and not cached ones.

something like this perhaps? :

mynntp.getcapabilites(refresh=True)