test: change SMTP_NO_MX_LOOKUPS to true

Testing with MX lookups disabled (true).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

asciinema/compose.yaml

@@ -21,7 +21,7 @@ services:
       SMTP_SSL: true
       SMTP_AUTH: always
       SMTP_RETRIES: 1
-      SMTP_NO_MX_LOOKUPS: false
+      SMTP_NO_MX_LOOKUPS: true
       MAIL_FROM_ADDRESS: ${EMAIL_FROM}
       MAIL_REPLY_TO_ADDRESS: ${ASCIINEMA_MAIL_REPLY_TO}
       SIGN_UP_DISABLED: ${ASCIINEMA_SIGN_UP_DISABLED:-false}