Echosign wasn't found at echosign.com

Whenever I send something out to get signed, I receive a  Postmaster error saying that echosign wasn't found at echosign.com.

I've not received this error before, until yesterday. Nothing has changed with the account, other than this. Sometimes the e-mail is still sent to the recepient and I don't receive an error.

Anyone experienced this before, and how did you fix it?