[baudehlo]

Spam, generally.

Because email uniquely among communication protocols allows sending a message without any previous agreement from the recipient, will always be susceptible to spam (and getting rid of that feature would destroy emails benefits).

Plus people want to filter differently. People deal with their inboxes uniquely.

[hackuser]

Why can't the universal mail client I propose have a spam filter? More likely, my incoming mail server will have the spam filter; the client will have the spam folder. What does it matter if only SMTP messages end up in that folder?

> Plus people want to filter differently. People deal with their inboxes uniquely.

That issue affects every messaging client's filtering. How does it affect a client any differently if it combines, for example, SMTP and SMS?

[baudehlo]

Oh you absolutely can, but there are a mix of problems some of which makes spam filtering better on the server (knowing bad sources of email, like infected desktop machines), some of which makes filtering better on the client (like knowing your users' preferences for what they consider spam).

There's a huge long history of very smart people (not even including myself in that list - I've worked with some people MUCH smarter than myself on this) working on this problem, including the very creator of this site, pg himself, and even he doesn't consider this a solved problem. People are still paid well to combat spam every day on behalf of demanding customers (and I'm grateful I'm not one of them any more) and it will always require new techniques and new input. Hopefully you will contribute too.

[baudehlo]

Oh and in terms of the other question: how many people get enough SMS messages that they want to filter them? Filtering is uniquely suited to a non realtime messaging system. Like email. I don't want to filter Slack/IRC messages either. I just ignore what I didn't read.