I can cover a few:
Database – If your site is configured to use a hostname for a database, and that hostname is set to 
, it won’t connect. Cloudflare doesn’t proxy database connections. I generally use ‘localhost’, or you can try a direct connection to the IP address of the database server.
524 – The server didn’t respond within 100 seconds: Community Tip - Fixing Error 524: A timeout occurred
508 – Dunno. Sounds like a server issue.
MX Toolbox – Cloudflare uses their own serial number format. Not a problem. Expire 604800. TTL is about half of what toolbox wants. Also not a big deal…it will just refresh faster.