Are you frustrated by an SPF record that is not valid?
One of the most common reason an SPF record will break is because it is including too many mechanisms.
Are you looking for a quick win to make sure your SPF record is valid?
Don't use the include:salesforce.com mechanism but instead use the include:_spf.salesforce.com mechanism.
This reduces the number of look up mechanisms being included from 8 to 2!
And using include:salesforce.com approves Gmail IP's which does open your domain up for spoofing across the Gmail network.
The Salesforce Help article also makes this recommendation:
Reach out to Marketo Support if this doesn't solve your SPF anguish. There are SPF experts at Marketo at Marketo who can get you on a path of Validation.
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