- Short answer
- Yes — Checkout Blocks' address format validation can block PO box shipping addresses; Shopify's pages conflict on whether it needs Plus.
- Where to set it
- Checkout Blocks app > Functions > Create function > Validation > Address format validation
- Address types it blocks
- Includes diplomatic, military, parcel locker, PO box and USPS gopost addresses
- Before it works
- A new function saves as Inactive — switch it to Active
- Scope
- Shipping addresses only; all markets by default, or the region markets you add
- Plan
- Changelog says all merchants; the Checkout Blocks overview says Plus — confirm in your admin
- Old Address Blocker
- Help page: removal September 30, 2026; changelog: August 31, 2026; not offered in our dev store on October 24, 2026
- Not in the new rule
- Block non-ASCII characters and Require street number
How does address format validation block PO boxes?
The address format validation function blocks checkout when a shipping address doesn't match your required format; Shopify's own example is PO boxes, so orders go to physical locations. Its Block specific address types rule stops addresses “including diplomatic, military, parcel locker, PO box, and USPS gopost”.
- Apps
- Checkout Blocks
- Functions
- Create function
- Validation
- Address format validation
It covers all markets by default, or only the region markets you add. As of October 2026 it validates shipping addresses only, not billing, and the customer must fix a flagged address to continue.
Which Shopify plan can use address format validation?
Shopify's pages disagree. The June 17, 2026 changelog says it “is now available to all merchants.” The Checkout Blocks overview says “All other features of Checkout Blocks are available only to Shopify Plus” beyond two content blocks, and the App Store listing names it among Plus extensions in its description, while its feature list shows address format rules without a Plus label. The function's own help page, read October 24, 2026, names no plan.
A Basic-plan development store we checked on October 24, 2026 showed no Plus or upgrade label on the option. That isn't proof for a production plan, so open the same path in your own admin and check whether the option shows a Plus or upgrade label.
What happened to the Address Blocker?
Shopify's help page, read October 24, 2026, still says the deprecated Address Blocker is scheduled for removal on September 30, 2026; the Checkout Blocks changelog post set its sunset for August 31, 2026. In a development store we checked on October 24, 2026, it was no longer offered as a block type.
Compatible rules were set to migrate automatically by the end of July 2026, per the help page. Two old rules aren't available in address format validation: Block non-ASCII characters and Require street number. If you relied on either, check what your function now blocks. For non-ASCII characters, the function's help page points to a custom validation rule.
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