Document what we consider to be good and bad phone numbers, email addresses and postal addresses

source/client_template.html.md.erb

@@ -6,6 +6,7 @@ parent: https://www.notifications.service.gov.uk/documentation
 <%= ExternalDoc.fetch(repository: repo) %>
 <%= partial 'documentation/testing' %>
 <%= partial 'documentation/api_keys' %>
+<%= partial 'documentation/recipients' %>
 <%= partial 'documentation/limits' %>
 <%= partial 'documentation/callbacks' %>
 <%= partial 'documentation/architecture' %>

source/documentation/_recipients.md

@@ -0,0 +1,59 @@
+# Recipients
+
+Notify won’t let you send messages to email addresses, phone numbers or
+postal addresses that aren’t in the right format.
+
+It tries to be as forgiving as possible.
+
+## Email addresses
+
+### Some good
+
+- test@example.com
+
+### Some bad (with reasons)
+
+- test@example
+
+## UK phone numbers
+
+### Some good
+
+- 07900900123
+- 07900 900 123
+- (0)7900-900-123
+- 447900900123
+- +447900900123
+
+### Some bad (with reasons)
+
+- 07900 9001 (not enough digits)
+- 07900 90012345 (too many digital)
+
+## International phone numbers
+
+### Some good
+
+- +1 etc
+
+### Some bad (with reasons)
+
+- 123 (not enough digits)
+
+[Link to countries](https://www.notifications.service.gov.uk/pricing#international-numbers)
+
+## UK postal addresses
+
+### Some good
+
+- example
+
+### Some bad (with reasons)
+
+- example
+
+## International postal addresses
+
+### Some good
+
+### Some bad (with reasons)