Since then, Congress has created additional restrictions enforced by a bipartisan group of lawmakers. Now, members can only send mail within their districts, and they have spending budgets that must be disclosed to the public. The ban on sending mass mail before elections also increased from 60 to 90 days, according to the Congressional Research Service.
As that deadline passes this election season, it's not yet known if members have sent a last-minute flurry of mailers, since spending totals for August won't be available until later this year. But the most recent data available suggest vulnerable members, as ranked by the Rothenberg and Gonzalez Political Report/Roll Call race ratings, still have something to be gained from franked mail, in spite of the changes.
On average, members running for re-election in non-safe districts spent $172 per day on mail franking. That's far more than the $63 per day that members in safe districts have spent.
Three of the top four spenders on mail between January 2015 and March 2016 are running in some of the most vulnerable districts in the country: Republican Reps. Rod Blum in Iowa's 1st District, Frank C. Guinta in the New Hampshire 1st and Will Hurd in the Texas 23rd.
Jay Ruais, chief of staff for Guinta, said the congressman is "committed to openness and transparency, including communicating our efforts on behalf of Granite Staters, important at a time when many feel alienated from their federal government. As a result of our correspondence, constituents have offered ideas for legislation that Rep. Guinta introduced in Congress, and a few have even been signed into law."
Rachel Holland, press secretary for Hurd, said: "As a representative for one of the largest geographic and rural districts in the country, Rep. Hurd utilizes a number of outlets to regularly communicate with constituents."
Every member of the House running in a district that is not safe has spent at least $2,000 on mail so far this Congress, and combined they've spent over $2 million.
In total, House members spent about $6 million on mail franking in the first quarter of 2016. Senators also have the mail franking privilege, but the chamber publishes its spending information in a way that's more difficult to analyze; this information was not included in Roll Call's report.
None of the bottom 50 House spenders on mail franking are from competitive districts. The member who spent the least in a competitive district was Rep. Brad Ashford, D-Neb.
For nearly all members, this spending represents a small portion of their total office budgets. Since everything from water bottles to staff salaries come out of the same account, known as members' representational allowances, mail franking typically amounts to a very small proportion of a members' total spending.
But it's not always that way.
Blum, the Iowa Republican, spent the most of any House member on franked mail and the least on staff. His office did not respond to multiple requests for comment for this article, though he dismissed criticism of his mailers in an interview with local ABC affiliate KCRG.
"What they do is let the voters in my district — there are 20 counties, a lot of them are very rural — let them know what we're doing," Blum said. "Letting people know about our veterans care fairs, senior wellness fairs and our job fairs."
A franking commission of six House members has to sign off on all pieces of franked mail before they're sent, and there are measures in place to ensure members can't use their mailing privileges to bolster campaigns.
Members aren't allowed, for example, to make partisan points or criticize their colleagues in franked mail. Specific guidelines dictate how many times members can mention themselves (eight times per page), and how big photos of the member can be (six square inches on an 8.5-by-11-inch piece of paper).
Members are explicitly banned from referring to their future congressional careers ("If I'm re-elected ..."), too.