I agree that other nations did not declare the Confederacy to be "illegal." The issue of legality seemed to remain an interpretational matter of the Constitution between the Union and the Confederacy.

A few of the articles I have run across about Confederate diplomacy mention that Southern officials in England and, I believe, France were met in an "unofficial" capacity. In other words, while Confederate diplomats were not kicked out or detained, they were not granted formal or official recognition by European governments. They often relied upon friendly European intermediaries to petition various government officials. I could not find information explaining the exact situation, but many historical accounts I pulled up do specifically say that diplomatic relations between the Confederacy and at least some European nations were done either in secret or unofficially. Do you have any information on this?