Make a test invoice to yourself and click "save and send."   After the pop-up appears, click the drop-down arrow to the right of the "from field" and you will see an options to "add gmail address,"  click this option.  Go through steps to add gmail address, save.  Now for all future invoices the "from" field will default to the gmail business address you added, which is FAR less less likely to go to your customers spam folder.  It took us a year to figure this out and probably some lost revenue since there is no telling how many customers thought they were being ignored since the default "intuit" from address was going to their spam folders.