First, some background information:
A year ago I started the construction of a software solution for creating and hosting time-controlled 'configurations'. A configuration contains similar representations of phidgets and their ports. It also contains 'interaction designs'. These are designs of what happens with outputs when analog or digital inputs change. Basically you place inputs and outputs on a canvas, drag connections between them and specify a formula for the behaviour, like "analog input value > 50 = output goes on". After a design is finished you can put them into timelines. so the can be set to run for a (in)finite amount of time.
When running a configuration (or specifically: its timelines), all is driven by a managing object - called a 'machine' - which uses a couple of timers to make things happen. You can specify min/max thresholds for analog input values. When those values are surpassed, an e-mail should be sent. Settings like the smtp server, the port, credentials and if SSL should be used are in the app.config file. All works fine in Windows.
When the configuration is finished, you can save it to a file, so you can put that on an SBC.
A second part of the solution is a Mono-compiled application built for the SBC. This application can run a configuration file. It hosts a Nancy FX webserver on port 6969 for visual feedback and control (which works fine). However when I trigger a mail by surpassing thresholds, no mail is sent. I know the mailing mechanism is hit because the code is an exact DLL-copy of the Windows version, compiled for Mono. I don't know a lot about Linux nor networking, but it almost seems like port 587 is blocked. I searched Google for a while. Couldn't find what I was looking for. So I have to ask...
If I'm right about the port being blocked: is there a relatively 'easy' way to unblock port 587 (as a start)?
If I'm wrong: can I send e-mail from code at all (because "ssmtp" and "WhatsApp" aren't viable options for me)?
However the outcome of this post, thanks for reading...!
PS: I'm Dutch: that's the reason for any weird sentences.