In Email sending protocol ( SMTP) , by the nature of it, there is no way of validating the sending address aka the FROM address. This can lead to many fraudulent activities. E.g Someone pretending to be you may email your bank spoofing your email address and steal confidential information or perform transactions.
SPF (Sender Policy Framework) is a solution introduced in 2006 in an effort to solve this problem of email senders authenticity. SPF describes a DNS record in a special format to list all the domains allowed to send mail from the domain. This allows spam filters to easily check if the origin of an email is from an authorized domain.
In most practical scenarios, email server IP address is different to the main domains IP address.