how do you know you're following "the" RFC correctly? And which one is that? There are several different standards just for email addresses themselves, which almost everyone gets wrong. Did you know addresses can have quotes and parentheses in them?
I didn't know at first and it was hell as when I first delved into this I thought it would be a simple task as it would be some agreed upon standard like JSON behind the scenes, but from what I understood emails were created a long time ago and some providers did things differently.
The majority of the work was done through testing lots of emails and I must have sent at least a thousands emails to myself from different providers and sites.
I've deleted the bookmarks in an attempt to reduce the PTSD it caused, but I think the main one I visited was RFC 1341 as I had some difficulties understanding the boundaries and encoding.
What was really tricky is getting it to work with all the different types as some emails didn't have boundaries while others had them, some were encoded entirely in base64, some partially, some of them were just plaintext, others were HTML while some were mixed or even offered multiple versions depending on what the email client supported.
Best thing is honestly to try it out and just pick a random address and send a really tricky email to it, would love to see you break the parser and telling me so I can improve it.
