There is an SPF record but it has too many lookups in this day and age where we have email servers, cloud email filters, ticketing systems, marketing systems etc all requiring to be part of the SPF. 

Quickbooks should use a DNS flattening service themselves and give us the SPF. 

For Payslips, why not let us use the standard Quickbooks email that quotes and invoices gets sent out from instead of having to use our own domain, this would at least be a work around?

I'm changing my DMARC policy to quarantine just to get my employees their payslips and tell them to look in their Junk.