Claude invented an email bounce from a dramatic tool result

What the research found

A small company's Claude sales agent told a visitor their email had bounced after a tool result reading "NOT SENT" was phrased dramatically; neutral wording fixed it, and the team now keeps tool results plain. The fix for fake domains was an MX DNS check in code, failing open on timeouts.

Claims and how well the evidence supports them

1. A tool result saying NOT SENT domain cannot receive email led Claude to tell a visitor their email had bounced when nothing was sent 98%
2. Rewording the tool result to neutral plain facts fixed the bounce narrative 98%
3. The fix for fake email domains was a DNS MX check in code before tool calls that create records, failing open on timeouts 98%

Evidence

• reddit.com https://reddit.com/r/ClaudeAI/comments/1xbipii/claude_invented_an_email_bounce_that_never

Actionability rated high.