I don't understand why his keepalive requires the extra spaces...and I'm not 100% sure that accepting them will fix the problem, though in theory it should.  I still lean toward making the spaces fix in imaplib, based on the postel principle.  I'd prefer to have a unit test, but if you or I or someone else doesn't get around to writing one before the next time we start working on releases, I'll probably commit the (pretty much obviously correct) patch without a test.