Disallow multiple SPF records
At the moment it is possible for customers to add more than one SPF record making the configuration invalid.
Plesk should disallow multiple SPF records.
Plesk should give an error and an automatic merge suggestion.
"Error you can only have one SPF record."
This is your current SPF record: <current SPF>
You tried to add: <extra SPF>
automatic merge suggestion: <combined suggestion>