If we’ve told you once, we’ve told you a thousand times—the feds can (and do) easily access your e-mail. In fact, sending materials through the United States Postal Service is legally more secure than e-mail.

On Wednesday, as the result of a Freedom of Information Act request, the American Civil Liberties Union has published the first public copy of the 2012 edition of the FBI’s Domestic Investigations and Operations Guide. And this document clearly draws that distinction. The new disclosure shows that the FBI believes it does have the authority to open your e-mail essentially whenever it wants:

18.7.1.3.4.3 (U) MAIL OPENINGS (U) Mail in United States postal channels may be searched only pursuant to court order, or presidential authorization. United States Postal Service regulations governing such activities must be followed. A search of items that are being handled by individual couriers, or commercial courier companies, under circumstances in which there is a reasonable expectation of privacy, or have been sealed for deposit into postal channels, and that are discovered within properties or premises being searched, must be carried out according to unconsented FISA or FRCP Rule 41 physical search procedures. 18.7.1.3.4.4 (U) COMPELLED DISCLOSURE OF THE CONTENTS OF STORED WIRE OR ELECTRONIC COMMUNICATIONS (U) Contents in "electronic storage" (e.g., unopened e-mail and voice mail) require a search warrant. See 18 U.S.c. § 2703(a). A distinction is made between the contents of communications that are in electronic storage (e.g., unopened e-mail) for less than 180 days and those in "electronic storage" for longer than 180 days, or those that are no longer in "electronic storage" (e.g., opened e-mail). In enacting the ECPA, Congress concluded that customers may not retain a "reasonable expectation of privacy" in information sent to network providers. However, the contents of an e-mail message that is unopened should nonetheless be protected by Fourth Amendment standards, similar to the contents of a regularly mailed letter. On the other hand, if the contents of an unopened message are kept beyond six months or stored on behalf oft he customer after the e-mail has been received or opened, it should he treated the same as a business record in the hands of a third party, such as an accountant or attorney. In that case, the government may subpoena the records from the third party without running afoul of either the Fourth or Fifth Amendment. If a search warrant is used, it may be served on the provider without notice to the customer or subscriber.

Here’s what all that means: under the much-maligned (but frustratingly still-current) 1986-era Electronic Communications Privacy Act (ECPA), law enforcement must get a warrant to access e-mail before it has been opened by the recipient. However, there are no such provisions once the e-mail has been opened or if it has been sitting in an inbox, unopened, for 180 days. In March 2013, the Department of Justice acknowledged in a Congressional hearing that this distinction no longer makes sense and the DOJ would support revisions to ECPA.

If that weren’t complicated enough, one United States circuit court of appeals decided that federal authorities do need a warrant before accessing e-mail. The case, known as United States v. Warshak, has created a split as other circuits haven’t yet taken up the issue, including the United States Supreme Court. (Google has since taken the public stance that it will follow the Warshak standard.)

The ACLU has been at the forefront of trying to figure out exactly where various federal agencies stand in observing or not observing the Warshak standard. Just last month, the advocacy group unveiled the fact that the Internal Revenue Service believes it has the authority to investigate tax cheats under ECPA, but soon after the interim director said the agency has never done so.