Ive been long time holder of the Nebraska Firearm Purchase Certificate, or "Blue Card." Likewise, have also held a Nebraska Concealed Handgun Permit since 2007. Belt+Suspenders kind of thing, I guess.
Same as you, I've noted the "by mail" provision in the Nebraska statute, but have always applied for the certificate in person. What the heck, you have to go to the sheriff's Office to obtain the application form anyhow. And I've never known of anyone else who actually has applied for the Blue Card certificate by mail. Fewer and fewer folks seem to apply for the Blue Card, perhaps preferring to use their NE CHP instead for their handgun purchases.
I'll always remember my very first visit, when a Douglas County plain-clothes deputy, after asking me why I was at the sheriff's office, said to me, "You have absolutely no business with something like that".
And I've noticed that some sellers are asking for either an NE CHP or Nebraska Firearm Purchase Certificate in order for a purchase to buy a rifle or shotgun. So far as I know, there is no requirement whatsoever for a Blue Card to be involved in a long gun transaction in this state.
Further, I'm guessin' that if anybody applies to the Omaha Police Department for a Blue Card, they get a stony look and are then told to go to the Douglas County Sheriff's Office.
I'm thinkin' we ought to get one of our frequent Forum posters to try out some of this application stuff and then report the results back here for discussion.
FWIW