Domain checker warnings explained

What the warnings in MxToolbox-style domain health reports really mean, which ones hurt email delivery and which are harmless, and what to do. Checked against the list operators' own pages, the RFCs and live DNS.

• SOA Serial Number Format is Invalid – Harmless on managed DNS
• SOA Expire Value out of recommended range – Harmless on managed DNS
• Blacklisted by SEM FRESH – Expires by itself
• Blacklisted by SEM URIRED – Minor; request removal
• The remote server returned an error: (308) Permanent Redirect – Not a site problem
• [SUPPLEMENTAL] Brand Logo not appearing in inboxes – Optional
• Listed by CSS (Spamhaus ZEN 127.0.0.3) – Real – fix before sending
• Listed on UCEPROTECT Level 3 – Usually ignore

Check what actually matters for delivery