Tracking link maker

How it decides

• It cleans the number first: spaces, dashes and a leading "Tracking #:" go; a pasted carrier link gives up the number inside it. A USPS barcode scanned with its 420 and ZIP code in front is cut back to the 22-digit number.
• Then it tries each carrier's format and check digit. UPS 1Z numbers, USPS 20, 22 and 26-digit numbers, FedEx 12, 15, 20, 22 and 34-digit numbers, DHL Express 10 and 11-digit waybills and international postal items (RB123456785GB) all end in a check digit, so a mistyped character is usually caught. Formats and test numbers come from the open tracking_number_data definitions.
• All-digit numbers can fit two carriers. A 22-digit number starting 92 can be USPS or FedEx SmartPost (which USPS delivers, so the USPS link works). Canada Post and Australia Post domestic numbers have no check digit we can test, so they are a guess from the length. When the label says the carrier, pick it in the list.
• An international postal item ends in the country of the post office that issued it: US, GB, CA, AU and IN get their post's link. Others are tracked on that country's post site or the destination's.
• India Post has no link that takes the number, so the email gets the number as text and the tracking page's address.
• The button is a one-cell table with the colour on the cell, so it keeps its colour in Outlook for Windows, which ignores padding and backgrounds on links. The tracking number goes under it as text for anyone whose email hides buttons.
• Open one link from your phone before you change carrier or template. USPS and Royal Mail refuse automated checks, so we tested those by hand.

What else the shipped email should say, and the emails for a late, held or returned parcel: Your order has shipped: the shipping email a small shop sends. If the link gets rewritten into a long redirect by your email service: what click tracking does to your links.