I am currently developing an application that parses and manipulates MIME messages wherein these messages are a central part of the domain model. Although I have already implemented the required functionality, for the moment, for parsing these messages, it seems unnecessary trying to reinvent the wheel would I need to add additional MIME features in the future. I could simply use an available library such as MimeKit which probably does the job much more efficiently and seems like the more robust way to go with. At the same time I feel hesitant to this idea for a couple of reasons:
I am fairly new to software architecture but what from what I've gathered online the consensus seems to be that the domain objects should not have any external dependencies since they model a domain that is specific to the business. And so if the business rules change it wouldn't be a good idea to have your domain model be dependent of an external library. However, since MIME is a standardized protocol this shouldn't be a problem, but that leads to the second point.
Although MIME is a standardized protocol, it has come to my knowledge that the clients from which my application receives these messages does not always fully conform to the RFC specifications. I have yet to come across a problem regarding the MIME format of the messages but with that in mind I feel as though there's no guarantee that I won't stumble across problems down the line.
I might have to add additional custom functionality regarding the parsing of the messages. This could however be solved by adding that functionality on top of the imported classes.
So my questions are:
Would it under normal circumstances be a valid alternative to use an external library for standardized protocols as a part of the domain model? It doesn't seem right to sully my domain- and application-layer with external dependencies.
How should I go about this problem with regards to my circumstances? Should I create an interface for the domain model so that I can swap it out with another implementation if needed in the future? This would require isolating the external dependencies in a class and mapping all the data to fit the contracts for the application layer which almost seems like more work than implementing the protocol myself. Or should I just implement it myself and add new features successively just to make sure that I have full control of the domain model?
I would highly appreciate your input.
Your entire question boils down to the following flawed thinking:
I am fairly new to software architecture but what from what I've gathered online the consensus seems to be...
Why let consensus make your decisions for you?
Who are these people who make up this "consensus"?
How do you know they have any idea what they are talking about?
Trusting the consensus of unknown sources seems like a terrible way to make decisions for your project.
Do you want to write software that solves real problems? Or do you want to get lost in the weeds of idealism and have your project fail before it even gets out of the design phase?
Do what makes sense for you.