In the first case, domain 2's SPF record is included in the SPF record for domain1, but can still be modified eg by adding another A host that isn't permitted for domain2.com:
Here a short summary with the example, include will be used when your mail hosted on other servers eg: Gsuite Zoho or other email providers the format is "v=spf1 include:serverdomain.com include:_spf.google.com ~all"
and redirect is used to redirect your mail from the main server to another domain server. eg: "v=spf1 redirect=_spf.mailhostbox.com"
You can also use the best method to cover all type of configuration: "v=spf1 +a +mx +ip4:192.168.1.2 ~all" Where +a indicate A RECORD of your domain, +mx cover MX record and IP cover IP address of your server. (note replace your server IP)
Pretty much what it says on the tin.
In the first case, domain 2's SPF record is included in the SPF record for domain1, but can still be modified eg by adding another A host that isn't permitted for domain2.com:
In the second case, domain2's SPF record is used as the complete SPF record for domain1, and no further modifications are possible.
Here a short summary with the example, include will be used when your mail hosted on other servers eg: Gsuite Zoho or other email providers the format is "v=spf1 include:serverdomain.com include:_spf.google.com ~all"
and redirect is used to redirect your mail from the main server to another domain server. eg: "v=spf1 redirect=_spf.mailhostbox.com"
You can also use the best method to cover all type of configuration:
"v=spf1 +a +mx +ip4:192.168.1.2 ~all" Where +a indicate A RECORD of your domain, +mx cover MX record and IP cover IP address of your server. (note replace your server IP)