To resolve the MXToolbox SPF record DNS lookup limit exceeded error, several strategies are recommended. The primary approaches include reducing the number of 'include' statements in the SPF record, which can be achieved by removing unnecessary or redundant includes, flattening the SPF record by replacing 'include' statements with direct IP addresses, and utilizing subdomains for different email sending services, each with its own SPF record. It's also crucial to use as few includes as possible, ensuring that only domains actively sending email on your behalf are included, and to be aware of the potential maintenance overhead of flattening SPF records due to IP address changes.