SPF records are limited to 10 DNS lookups to prevent Denial of Service (DoS) attacks. Exceeding this limit causes SPF validation to fail.
The "include" mechanism tells the receiving server to check another domain's SPF record for authorized IPs (e.g., include:_spf.google.com).
"-all" is a Fail (reject unauthorized mail), while "~all" is a SoftFail (accept but mark as Spam).
SPF protects your domain from being used in email spoofing and helps improve your email deliverability.
No, a domain must only have ONE SPF record. Multiple records will cause SPF to fail.