The Yahoo email problem
don't use yahoo for any important business or personal email.
There has been a problem with Yahoo email services since around 26. Recently it has increased considerably. Yahoo typically defers a large part of the email sent to it, then sometimes lets it thru on second submission, or overnight when it is quieter, and often just rejects it altogether.
Yahoo mail denies the first delivery attempt of an email (451 Message temporarily deferred - 4.16.5. They assume that SPAMers don't try sending the same email twice, so they put the ip address of that email server on a list and then if the delivery is retried within a short amount of time, they assume that it is a good email. This is a pretty stupid policy and it meeting with complaints from all over the world.
Yahoo publishes what you should do about this, and directs you to a page where you whitelist your servers, unfortunately though, there isn't much evidence that anyone at Yahoo ever reads your submissions, since all you get is an auto-response.
They also advise that you use SPF records and domainkeys or DKIM. But there isn't a great deal of evidence that these practices help much, since they also defer signed domainkeys email, and appear to ignore SPF records. Some people suggest that yahoo are refusing as much as 15px;% of all email sent to it. SPF records, which we use, are at least an open system. Domainkeys are a proprietary system (a yahoo proprietary system) that is unwieldy and difficult to use. And the evidence is that Yahoo also defers DK signed email, or consigns it to their spam folders. Frankly Yahoo email administration is not up to scratch.
So what's the answer? Unfortunately the only one I can think of is,
don't use yahoo for any important business or personal email.
