Gmail denies emails

When we try to send email to Gmail accounts, it is returned as undeliverable, with instructions to set up DKIM or SPF records. This NEEDS to be addressed and fixed!

UPDATE:

So I did find Homesteads recommended DNS Record values, and compared them to what we have. We haven't touched the settings since we first had it set up by Homestead, but when I checked, it seems that Homestead updated things on their end, and our settings no longer matched. So... check your DNS records, update them if necessary, and see if it solves anything? Thus far it seems to have cleared up some of the rejected notices we are getting...