The four groups
HTTP 4xx reasons
NOT FOUND · FORBIDDEN · UNAUTHORIZED · TEAPOT
Status 418 'I'm a teapot' is RFC 2324. It's a joke that became canon.
HTTP 5xx reasons
BAD GATEWAY · SERVICE UNAVAILABLE · INTERNAL · GATEWAY TIMEOUT
Email delivery failure modes
BOUNCE · SPAM · BLOCKLIST · GRAYLIST
Words paired with ERROR
TYPE · RUNTIME · SYNTAX · USER
Why this puzzle works
Friendly difficulty-2 warm-up. The trap is INTERNAL (server error) wanting to be a wordplay 'internal error' — it's not; it's a real HTTP 5xx phrase. The intended purple tease is USER ('user error' / PEBKAC). Most players solve yellow→purple→green→blue in that order; the email-delivery quartet is the least common knowledge but lands cleanly once everything else is gone.
How to read a Connectle without solving it
A code-themed grouping puzzle rewards counting as much as recognition. Start by listing every plausible group, then notice which tiles appear in two lists. Whichever group has exactly four unambiguous members is your anchor — solve it first and the rest of the board collapses by elimination. The hardest tier (purple) is almost always wordplay: tiles that share a prefix or suffix, not a concept. If a tile feels orphaned, ask whether the same word could follow or precede a common engineering word like root, stack, cache, or queue.