Is it possible to have users' email replies to case notifications attached to that case as a case comment? I've looked pretty much everywhere, and even asked Salesforce support but no luck, they just say you need custom coding but don't say where to start. Thanks!
Yes. Assuming you can forward a mailbox, you can do this with very little code.
Just be aware, you may need to tweak your configuration to avoid dual notifications now :-)
Edit: just did a sanity check per your comment... mine catches incoming replies ok:
So when the case owner sends emails, they're "from" the routing address which has a dedicated mailbox, eg
Reconfirming with the screenshot below, the nice short Email-to-Case address needs to be selected (From) when sending emails. Hopefully this addresses your comment about the users' send-to address.
From an engineering point of view, this whole function is pretty bang-bang out of the box. I'm surprised Salesforce don't crow about it more.
You would need to develop code around the EmailMessage object.
Basically, the idea would be a trigger that takes the reply ("BODY"), and copies that into the parent case comment.
Everything looks ok but do one thing -
Setup your email mail box email forwarding setting.
Set email as : email-to-case routing address
It helps when customer reply on this mail. It will automatically add case comment to this particular case