What is a flagged email?

What mechanisms, particularly those based on 'standards' (which could be industry group de facto standards), are of greatest use to email originators in assuring that legitimate email is delivered and traffic that 'spoofs' an email domain is at least flagged, if not blocked?

• This is a follow-up question to . Nick's response indicates that some vendors of technology or services may be claiming more for SPF and DKIM than is justified. If we limit the question to how originators of email can reduce the likelihood that their customers/clients will be spoofed or phished by email claiming to originate from a legimiate site, it would be instructive. Additionally, I'd like to raise the question of  whether intermediaries for large volume of email … Yahoo!, GMail, Microsoft … are making full use of DKIM and SPF.  If not, why not?

• Answer:

  SPF records is a given, add DKIM as well to your emails. DMARC is gaining a lot of traction with the large ISP I personally know. Email delivery is based on reputation, if you have none, delivery of your email will be challenging. You can use a variety of services to improve your delivery and getting the emails into the inbox, it's part science and part art (black box)