There are situations when a message will be silently lost and that is recognized in the specs. There are also MTAs that don't quite fully conform to the specs.

Why not have them resend? What prevents the sender you are dealing with from resending? (Assuming they even sent an e-mail the first time around.)

Expiry. Service is like fresh vegetables.

The Simple Message Transport Protocol defines how an email message is to be transported between servers. SMTP is about the processing between servers.

A fully-compliant receiving server is obligated to send a BOUNCE message if the recipient doesn't exist/has a full mailbox/is rejecting the message as spam or infected/several other conditions.

A fully-compliant sending server is obligated to report if it can't deliver an email for any of a number of reasons, including not finding the receiving domain or receiving a rejection from the receiving domain.

Those failures can be "temporary" (4xx errors), in which case the fully-compliant sending server will keep trying until its mail "queue" times out. That can be anywhere from a few hours to several days...length to be determined by the sending server [My server, My rules]

They can also be "permanent" (5xx errors), in which case the fully-compliant sending server will report the failure to the sender immediately.

All of that activity will be logged on both servers, but in a high-volume environment, will only contain a few hours of information, which, as has been pointed out, is likely to not be provided to anyone for a dispute of this type.

There are no guarantees implied or required. Even fully-compliant servers will occasionally have problems...and there aren't any email police out there in any event.

Consider that the S in SMTP stands for Simple...just sayin'

If you (anyone) really wants to understand how all this is supposed to work, review the links Turbocapitalist posted. They make good reading when you're having trouble getting to sleep

Given the timeline of this thread, it's unlikely that there's any information to be gleaned from either ISP at this point, IMO.

Isn't there a relatively recent law that forces ISP's to keep logs for much longer? Remember, we do not need to check for entire emails or even headers, just my email address NOTappearing anywhere in their logs is enough, to prove the sender's fraud.

Not that I've heard of, and my company provides email services. Again, there are no email police. The 'net is still free (so far)

There is such a law in England, are you sure there is no such law in the US? Here's the UK law:

https://www.theguardian.com/technolo...t-data-storage

...and what good will it do to discuss the topic with us, at length?
how's the actual issue coming along?

Someone who knows the law will say "the law of this state obliges them to keep records for X months of just the email addresses or something like that", and we then contact the isp armed with this knowledge so they either admit they do not keep email addresses and are acting illegally and risk trouble with the law or they confirm they keep records but won't release them to me, and then the sender's expected refusal to ask for their record from the isp to prove their innocence by giving it to paypal is evidence that they have fraudulently not sent the email and I get my money back from paypal and paypal gets the money back from them by chargeback.

GoDaddy is the host of the crook's site where emails come from, and the server is located in Arizona. It is a dedicated server where all 4 sites hosted are owned by the crook.

Any suggestions how to find out what the data detention laws are in Arizona and if GoDaddy complies, or leaves it up to their customers to comply?

Crucially: it will not be me but the crook who will be requesting the evidence to be passed on to paypal, which they won't because they never sent the email.

Just engage a good attorney to help you with this. Someone who is an expert in the relevant law. The fees that you pay him or her will be (tax-deductible ...) money well spent.

Don't continue to ask an Internet forum for advice on this matter: hire someone who truly knows, and do exactly what they say. Give them your "power of attorney" to act on your behalf.

The settling of a slightly-complicated estate was my first introduction to what attorneys actually do, and I have kept the same attorney(s) on retainer for more than twenty years since. "Let me ask Tom (and/or Hank) about that ..." Today, I frankly wouldn't think to do otherwise: the term, counselor, is very appropriate. You might think that you know where all the rocks are, but you have no idea.

Also, when someone starts to give you grief and you simply ask your attorney to send them a letter, sometimes their grief-making magically ceases.