SMTP not working since July.

This will be a 'long' post as I want to ensure as much detail as is possible is in here.

Mid July this year (2023), our in premise DocuWare started to intermittently stop sending emails. Towards the end of July it stopped all together. Since we are a reseller and also a user of DocuWare, I put in a quick workaround telling users to check Tasks daily. This allowed me time to dig in a look at the issue.
Our environment is stable. Our DocuWare instance has its own application server. The SQL is shared with another application - the SQL server has plenty of capacity. We use DocuWare for HR, Operations and Sales. We have workflows configured across the company - some are more critical than others. The critical workflows affect employees pay, PTO and various other things.
I am DocuWare certified. The training given was great but does not cover deeper troubleshooting with issues such as what we are experiencing - and that's not a criticism of the trainers or the training. It's a fact of ALL the document/content/records software on the market today.
We are resellers of DocuWare.  
I have opened 2 tickets with DocuWare ( SR-214888-J6T8R, SR-208008-H3G3S). On both occasions, the support tech has told me it is 'our problem and not DocuWare'. The first ticket was a straight back and forth collecting information to be told it was an SMTP issue and questioned our SPF record. The second ticket also involved a support tech doing a remote session without audio so I was unable to ask questions, testing SMTP using his personal Gmail account which did send an email, then telling me it was my issue and he couldn't help further. I have worked with our exchange provider (we use hosted exchange) and our outside I.T. contractor who assists with servers and infrastructure. They have all looked at the issue and cannot find a problem.
I have upgraded DocuWare to v7.8 in October in the hope that the upgrade might fix the problem. 
The issue is that we cannot send emails from DocuWare. I have spent *many* hours working on this. I have somehow managed to get 3 emails to send by some fluke but it was not repeatable. 
As I've stated above, I've spent hours troubleshooting this - I've tried multiple authentication methods, I've looked at IIS, checked firewalls, permissions, DW settings. We had no problems up until July. I know this was working with our hosted exchange provider. What I can't figure out is why it stopped working in late July.
I have reached out to our Regional Sales rep who had an internal resource ask for a lot of information to be told it was our issue. I got the email address of a developer at DW that was going to ask the US Head of Support to look into getting some help. 
As a 30-year Imaging professional with MANY years of customer support (both user and technical), to leave a customer with 'it's your problem' without any explanation of why or how to fix the issue, is a massive personal 'no-no' for me. If I'm working with a customer and find an issue that is our problem or the customer problem, without fail I will work to either provide options on a resolution and remain with customer to complete the fix or preferably provide a resolution myself. It maybe an issue that isn't directly part of the software, but going the extra mile for a customer makes a huge difference in the relationship going forward. I have been relentless in my handling of support for my customers. If this was a customer of ours that was using On Premise DocuWare and this issue had been on-going this long without resolution, I would expect the customer to have long since switched to another software.
I've attached screen shots of 3 of the logs I've submitted over the last few months. There are many different errors based on the troubleshooting I've carried out.
It is an SMTP issue. It may well be something on our side or it could be something with our provider or it could be a unique circumstance with DocuWare itself. What we need is a DocuWare expert that can help diagnose and explain where the breakdown is occurring and offer options to resolve. I can look at the logs all day but I am not manufacturer of the product and I do not possess the skills or information to completely understand what it happening. I am 100% sure there is somebody at DocuWare that can look at this issue and understand where the problem lies and how to resolve it. I can provide any and all information about our systems and configuration.
Maybe I'm missing something on the website, but options to contact technical resources at DW are not available and since opening a ticket has twice failed to resolve our issue, I'm now resorting to any method to get assistance.

Thanks

Hi David,

to me, these messages sound like your SMTP Server does not allow your DocuWare System to log in. That could have several causes, which I cannot read from the logs you provided.
Maybe the SMTP Server itself or some firewall in between your DocuWare Server and SMTP Server block traffic from everywhere except some whitelisted IP Addresses, maybe the mail account(s) you are using is missing SMTP permissons. It might even be an SSL problem regarding an expired certificate or one with an old, unsupported encryption type.
Also, in your last screenshot, you are using SSL with Port 587, however, 587 is default for TLS/STARTTLS, SSL default is 443. This might be intended, or might be an oversight, depends on your SMTP Server.

This is definitely either an SMTP Server issue or a network issue. If you want to test SMTP without the DocuWare overhead, it uses the NuGet Package "MailKit" Version 2.3.1.6 to send e-mails.

Hope this helps a bit.
Greetings from Germany,
Simon H. Hellmann
DocuWare System Consultant

Sorry, after taking another look, it is obvious that the SMTP Server is not on your network, but connected to via internet.
Have you already tried using tools like the Microsoft Connectivity Analyzer or mxtoolbox to check for connection issues?

Greetings from Germany,
Simon H. Hellmann
DocuWare System Consultant

Hi Simon.

Thanks for your reply.

Microsoft Connectivity Analyzer passes all tests.

mxtoolbox looks OK also but I don't have the purchased edition to dig deeper.

Thanks!

David Houlston
Imaging Specialist