My most determined emailer now suggests that if there is no explicit rule against plagiarism, then one can lift from a text at will. The emailer cites guidelines from Duke University:

Unless there is a clear indication that the content is in the public domain, or a blanket statement from the author that copies may be distributed without permission, you must assume copyright protection.

The correspondent then concludes: “If I read the information from Duke University correctly, than I don’t think there was any plagiarism.” However, a number of emailers poked holes in that argument before it was even published. “It’s plagiarism whenever you pass off someone else’s work as your own,” writes one:

The disclaimer on the dailykos site merely releases the borrower from any copyright concerns.