I reported this to ST on 4th Feb under 110-23EAE894-000B

Still no fix, we thought it was related to specific headers allowing emails to bypass filtering however it doesn't appear to be the case, we have scheduled a downgrade this weekend as ST don't appear to want to fix the issue.

:(

That is not encouraging, Chris. How are you doing a downgrade?

Makes me wonder why a company would post a minor upgrade and announce that it would be the last upgrade to v.16 and there would be no further bug fixes for that version when the upgrade has a VERY MAJOR BUG!!! Could it be they're trying to force everyone to upgrade to 17?

This is not a minor thing. Come Monday I'm going to have a lot of very unhappy customers calling about all the spam they're getting.

Uninstall current v16 then install the previous build, usual way of doing it. Its only a minor update so nothing should.... break :) Just make sure you have a decent backup.

I don't know why it has not been taken seriously.

We can't upgrade to v100 as the activation step during setup doesn't work, ST have provided a manual activation code which we will not use (as automated activation should always work), we asked for additional debug logging to be added but this has not happened yet. We suspect the issue is some sort of SSL issue based on the schannel errors, could be just the installer with the issue but we don't want to chance it. Ticket was raised 7th December, asked for additional debug logging on the 19th December, last reply 3rd Jan, ticket was closed sometime after that.

How do you get the previous build?

Not from ST website obviously, but as we often had to downgrade, we started archiving each build.

I made you a we transfer for the previous build 16.3.6915 (Dec 7, 2018):

https://we.tl/t-6ELK4nfFwA 

Thank you, Sébastien. Archiving builds is a good idea. I suppose we're just too trusting of companies who receive our money for the illusion of service and a dependable product. 

Yes. I've just re-read ST general provisions and as I understand they can't be responsible if the product we bought are not working as expected...

"SmarterTools makes no representation, warranty, or guaranty as to the reliability, timeliness, quality, suitability, truth, availability, accuracy, or completeness of the Service or any content. SmarterTools does not represent or warrant that the use of the Service will be secure, timely, uninterrupted, or error-free or operate in combination with any other hardware, software, system, or data; the service will meet Your requirements or expectations; "

Hello everyone, and thanks for reporting this issue. This was brought to our attention yesterday and has since been resolved. You can anticipate this fix in a minor release we'll be publishing soon (SM 16.) We apologize for any inconvenience this may have caused. 

Thank you, Kyle. My faith in humanity has been restored!