AADC mail is a category of presorted commercial mail in which letters and cards are grouped by the Automated Area Distribution Center that serves their destination, earning the mailer a discount on First-Class Mail or USPS Marketing Mail postage.1United States Postal Service. Domestic Mail Manual 245 Mail Preparation The postal service gives you the discount because you have done part of its sorting work before dropping the mail off. The more precisely you sort, the less it costs.
Where AADC Sits in the Presort Ladder
Commercial letter mail is sorted into a hierarchy that runs from finest to coarsest: carrier route, 5-digit, 3-digit, AADC, and Mixed AADC.1United States Postal Service. Domestic Mail Manual 245 Mail Preparation A 5-digit tray holds pieces all going to a single ZIP Code. A 3-digit tray groups pieces sharing the same first three ZIP digits. An AADC tray goes broader still, holding pieces bound for the entire service area of one Automated Area Distribution Center, which typically covers several 3-digit ZIP prefixes.
Presort software works down the ladder in that order. It pulls pieces into 5-digit trays first, then 3-digit, then AADC, and whatever remains falls into Mixed AADC.1United States Postal Service. Domestic Mail Manual 245 Mail Preparation Most mailings end up with pieces at several different levels. Deeper sorts mean deeper discounts, but only if you have enough volume going to the same place to fill the tray.
AADC vs. Mixed AADC
An AADC tray contains pieces all addressed to one Automated Area Distribution Center’s service area.2United States Postal Service. Domestic Mail Manual 235 Mail Preparation The postal service publishes labeling list L005, which maps each 3-digit ZIP prefix to its AADC. Mixed AADC is the catch-all tray: it holds pieces bound for two or more different distribution centers when none of them had enough volume for a dedicated tray.
For First-Class automation letters, an AADC tray requires at least 150 pieces for a single destination, unless it qualifies as an origin entry AADC tray, which has no minimum.2United States Postal Service. Domestic Mail Manual 235 Mail Preparation Pieces you cannot consolidate to that threshold roll up into Mixed AADC, which costs more per piece because the postal service still has to separate them by destination after accepting the mailing.
What AADC Postage Costs
The savings are the reason to bother with any of this. A single-piece First-Class letter at the retail counter costs $0.78. The First-Class automation AADC rate for 2026 is $0.641 per piece.3United States Postal Service. USPS Notice 123 – January 2026 Price Change That is roughly $0.14 per piece, which on a 10,000-piece mailing works out to about $1,400. Finer sort levels save more; Mixed AADC saves less.
USPS Marketing Mail automation rates run well below First-Class, and the exact per-piece price depends on presort level, entry point, and whether the mailer qualifies for nonprofit pricing. Current rates are published in Notice 123 on the Postal Explorer website.4United States Postal Service. USPS Notice 123 – Price List Check the current version before budgeting a mailing, because small rate changes multiply quickly.
The Minimum Volume to Mail Commercially at All
Before the presort levels matter, your mailing has to be big enough to qualify for commercial pricing in the first place. First-Class presorted and automation mailings need at least 500 pieces.5United States Postal Service. Domestic Mail Manual 233 Commercial First-Class Mail USPS Marketing Mail needs at least 200 pieces or 50 pounds.6United States Postal Service. Domestic Mail Manual 243 Commercial USPS Marketing Mail Below those numbers you pay single-piece retail no matter how well you sort.
The minimum applies to the mailing as a whole, not to each tray. A 500-piece First-Class mailing might have 200 pieces in 5-digit trays, 150 in an AADC tray, and 150 in Mixed AADC, and still qualify.
Physical Standards Every Piece Must Meet
Every piece claiming AADC automation pricing has to run through high-speed sorting equipment without jamming. Letters must be rectangular with an aspect ratio between 1.3 and 2.5 (length divided by height). Minimum thickness is 0.007 inches, rising to 0.009 inches for pieces taller than 4-1/4 inches or longer than 6 inches. Maximum size is 11-1/2 inches long, 6-1/8 inches high, and 1/4 inch thick.7United States Postal Service. Quick Service Guide 201 – Physical Standards for Commercial Letters and Postcards
Automation letters for First-Class Mail, USPS Marketing Mail, and Periodicals all cap at 3.5 ounces. Every piece must carry an Intelligent Mail barcode and have its address printed in the Optical Character Recognition read area using machine-readable fonts.7United States Postal Service. Quick Service Guide 201 – Physical Standards for Commercial Letters and Postcards
What Makes a Piece Nonmachinable
Pieces that fail automation standards get a nonmachinable surcharge that wipes out most of the discount you sorted for. A letter is nonmachinable if its exterior is not paper, if it contains rigid items like pens or keys, or if it has clasps, strings, or similar closures. Polywrapped or shrinkwrapped pieces also fail. The piece and its contents must bend easily enough to pass around an 11-inch-diameter drum under 40 pounds of belt tension.8United States Postal Service. Domestic Mail Manual 201 – Physical Standards Test your design against these standards before printing thousands of pieces.
Address Quality: CASS and Move Update
The discount is the postal service’s reward for clean, deliverable mail, and two separate address-quality rules apply.
CASS Certification
Any mailing claimed at an automation rate has to come from an address list coded with CASS-certified software.9PostalPro. CASS CASS (Coding Accuracy Support System) standardizes addresses and assigns ZIP+4 codes so the Intelligent Mail barcode can route each piece correctly. For non-carrier-route automation mailings, the coding must be done within 180 days before the mailing date.10United States Postal Service. Domestic Mail Manual A950 – Coding Accuracy Support System Carrier route mailings have a tighter 90-day window.
Move Update
Separately, the Move Update standard requires mailers claiming First-Class presorted or USPS Marketing Mail prices to show that the mailing list was updated within 95 days before the mailing date. USPS offers three pre-approved methods: NCOALink, Address Change Service, and ancillary service endorsements other than Forwarding Service Requested.11PostalPro. Move Update
Compliance is tracked through the Mailer Scorecard. A Move Update error is flagged when a piece’s address has not been updated even though a change-of-address record shows a move between 95 days and 18 months before the postage statement date. The allowable error rate is 0.5%, so even a small number of stale addresses in a large mailing can trigger penalties.12United States Postal Service. Publication 685 – Streamlined Mail Acceptance – Appendix A
Preparing and Submitting an AADC Mailing
Preparation starts with running your list through CASS-certified software and applying Move Update processing. Presort software then assigns each piece to a tray, working from finest to coarsest: 5-digit, then 3-digit, then AADC (using labeling list L005 to match 3-digit prefixes to distribution centers), then Mixed AADC for whatever is left.2United States Postal Service. Domestic Mail Manual 235 Mail Preparation
Each tray is labeled according to Domestic Mail Manual specifications and strapped for transport. Documentation goes on the appropriate postage statement: PS Form 3602-R for USPS Marketing Mail13United States Postal Service. PS Form 3602-R – Postage Statement USPS Marketing Mail or PS Form 3600-FCM for First-Class Mail and USPS Ground Advantage.14United States Postal Service. PS Form 3600-FCM – Postage Statement First-Class Mail
Commercial mail is taken to a Business Mail Entry Unit, where postal clerks verify barcode quality and match piece counts to the postage statement.15United States Postal Service. Where to Go to Drop Off Your Business Mail Payment usually runs through a permit imprint account, which carries a $370 application fee.4United States Postal Service. USPS Notice 123 – Price List Once verification is complete, the mail enters the postal service’s distribution network at the AADC rate you prepared it for.