Domain Keys aka DKIM aka DomainKeys Identified Mail, Sender ID and SPF aka Sender Policy Framework. Why all the AKA's? Different Web Control Panels or DNS consoles may label them differently.

Then check the server IP address to see if it's on a SPAM Blacklist (MXtoolbox). There are testing tools to help marketing people lower the SPAM score of potential campaign emails to ensure the email is delivered AND place in the user's Inbox.

See Sender ID [en.wikipedia.org] for Sender ID and links to other related resources. Sound like a lot of work just for email? Thank your neighbourhood SPAMMER for making all that necessary <G>

Hi Hoople -

Thanks very much for the information.

Digging back into ancient history, I've discovered that I implemented an SPF certificate which generally solved the problem.

Then this domain did get blacklisted because somebody hijacked their contact list - wow, what a nightmare that was.

Eventually got that fixed by paying for a service (I guess I can't mention the name here) but they provide a "whitelist of legitimate email servers to reduce spam filtering false positives. Cheap enough so my client went for it.

Anyway, appreciate your input... very informative.

FOLLOWUP QUESTION: So, is it a good idea to implement DKIM and Sender ID and SPF or is just one adequate? Your comment about "DNS consoles may label them differently" would lead me to believe that the best option is all three?

All three is preferable because the recipients vary in which checks they prefer to implement in acceptance testing of inbound emails. Doing less might potentially cause a portion of the email campaign to not make it into the recipients Inboxes or worse, be rejected.

From that service get the IP address of the configured sending servers to add to the email authentication solutions (SPF, DKIM, etc) above. You need to declare them as authorized to send emails on this domain's behalf.

The console mention was for clarification - I've seen both the acronyms and the full text descriptions in use.

Hi Hoople - Fantastic... thanks for the explanation - hope this will assist others as well with this question and task.

These aren't certificates. It's mostly making DNS changes to your domain or some mail-server settings.

Last time I did this (a long time ago) the list was:

• Sender Policy Framework (SPF) [openspf.org]
  
• SenderID [microsoft.com]
  
• DomainKeys [en.wikipedia.org]
  
• DKIM [en.wikipedia.org]

I recall DKIM was the most difficult to implement. However, if you're using one of the big free-mail providers like Gmail, Hotmail or Yahoo mail they already have this implemented for you.