Why don't I know more about computers?

I actually got a 'could not deliver' message on the e-mails I tried to send yesterday (or was it the day before?) to post an entry. And this is what it told me was wrong (address redacted for privacy reasons!)

#< #4.0.0 X-Spam-Firewall; host mail.livejournal.com[208.93.0.48] said: 450 4.7.1 <barracuda.city.org>: Helo command rejected: Host not found (in reply to RCPT TP command)> #SMTP#

Which, to me, just means this:

PPPPLLLLLLBBBBBBTTTTTTTHHHHHHHH!