Memo to politicians: When the election’s over, you can close up your campaign office, but you better keep renewing your domain name.

Case in point: Ed Perlmutter let his 2006 campaign site expire. A porn operator in Germany bought the expired domain name and put a porn and dating service on it.

The porn operator bought the name through Sedo, a domain-name and website “parking” service, headquartered in Germany with an office in Cambridge, MA . After a lot of aggravating phone calls back and forth between Perlmutter’s reps and Sedo, it looks like Sedo did the right thing.

“This content violates our policy, and we’re shutting down these sites as quickly as we learn about them,” [Sedo CEO Johnston said. “I just learned about this website today when I returned from lunch. We plan to shut it down this afternoon.”

But they may not have done it for that reason. Perlmutter’s reps claim Sedo first tried to sell them the domain back, increasing the price with each telephone complaint, until it reached $1,200. Then the Perlmutter camp threatened legal action.

We’d like to buy it back just to shut it down,” Chase said. “But we’re not going to be blackmailed by some pathetic cyberspace squatters. Evidently, they’ve done this to hundreds and hundreds of websites and put the exact same information up.

“There’s case law that prevents taking a website like this and directing it to their own website. One of our campaign lawyers has sent them a ‘cease and desist’ letter.”

Lesson learned.