Now you solved my mystery!
I will update my blog post soon.
Thank you!

This preference did not change in 853 I believe.

Every customer situation is different and, like you said, a lot is based on the number of PVUs that you are currently licensed for with Domino Enterprise Server (PVUs). So, each case has to be weighed carefully considering future expansion needs as well (such as adding additional Domino servers in the near future).

Lets take a generic 100 user Domino Enterprise case at MSRP with 2 dual-core clustered Domino servers (280 PVUs).
100 Domino Enterprise CALs Renewals ($42.75/each): $4,275.00
280 PVUs Domino Enterprise Server Renewal ($12.40/each): $3,472.00
Total Domino Enterprise Renewal 1 Year: $7,747.00
Total Domino Enterprise Renewal 2 Years: $15,494.00
Total Domino Enterprise Renewal 3 Years: $22,971.00

100 Domino Collaboration Express New ($160.00/each): $16,000.00
Domino Collaboration Express 1 Year: $16,000.00

100 Domino Collaboration Express Renewal ($41.50/each): $4,150.00
Domino Collaboration Express 2 Years: $20,150.00
Domino Collaboration Express 3 Years: $24,300.00

In the above case you would not break even until moving into the fourth year. This of course assumes that you won’t be needing any additional PVUs for additional servers within the 3+ years. If you wanted to add a Notes Traveler server, a BES Express Server, or a Mobile Connect Server within those 3 years, then you would need to purchase additional new Domino Enterprise PVUs for that server which would tilt the savings greatly in favor of Domino Collab Express.

However, currently there is a promotion by IBM where you can receive 15% off the entire software licensing cost for newly purchased Lotus Software licenses if you finance the purchase through IBM Global Financing (http://www-01.ibm.com/software/lotus/offer/pricing.html) and you exceed the minimum of $5000.00. This should apply to your case, so your total licensing cost would then become:
100 Domino Collaboration Express New ($160.00/each): $16,000.00
Domino Collaboration Express 1 Year with 15% savings: $13,600.00

100 Domino Collaboration Express Renewal ($41.50/each): $4,150.00
Domino Collaboration Express 2 Years with 15% savings: $13,600 + $3,527.50 = $17,127.50
Domino Collaboration Express 3 Years with 15% savings: $20,655.00

In the above case with the 15% off IBM promotion you would actually be better off with Domino Collab Express by the third year ($20,655.00 vs. $22,971.00 [Enterprise]).

In another example where you had 2 quad core clustered Domino servers then your 2 year renewal fee for Domino Enterprise Server would be $22,188.00. So you would be better off with Domino Collab Express by the second year because that would only be $20,150.00 (before counting in any potential promotional savings).

So here are the numbers you asked for. I hope this was helpful. If you’d like to talk directly with us about this please don’t hesitate to contact us (sales@caicorp.com or 888-614-2197).

When you say that Express is a moving target what do you mean exactly? This most recent licensing change has not affected current licensed users in any way. In fact, it has only improved their ability to take full advantage of the capabilities of Domino. Could you be more specific about what you mean by moving target? Thanks!

Thanks.

Looks like SMTPClientDebug=x is to troubleshoot outgoing SMTP whereas SMTPDebug=x is to troubleshoot incoming SMTP dialogue.

set config SMTPDebug=x (where x is 0, 1, 2, 3 or 4)
set config SMTPDebugIO=x (where x is 0, 1, 2 or 3)
set config SMTPSaveImportErrors=x (where x is 0, 1, 2 or 3)

Below is also helpful for debugging Notes Mail routing.

Tell router c > In place compaction of the mail.boxes.
Tell router d > Shows message detail (sizes, times, and hop).
Tell router e > Exits the router (same as q).
Tell router l > Lists the messages in queue and the routing state.
Tell router m > Shows memory usage by the router.
Tell router o > Lists the out of office details.
Tell router p > Pauses the router.
Tell router q > Quits the router (same as e).
Tell router r > Resumes the router from a pause state.
Tell router s > Shows the router queue state (delivery , transfer, dispatch and sweep threads).
Tell router update config > Updates the routing tables.

It would also be useful if you increase the log treshold (set config) as shown in my blog post. The log will tell you more in depth what the specific policy is rejecting it. Until then, it is hard to find out the cause of the email rejection.