>you will not be able to receive/access emails that are sent to your primary address/domain until the provider resolves their issues.

You won't be able to receive new e-mails, but if you use a local client like thunderbird, you can still access your old e-mails.

With slack down, I can only access the messages that I (luckily) have cached locally.

Except that email has built in retries and feedback. Also it's expected to be async, so if a server is down for an hour, most people don't even notice.

> email has built in retries and feedback

Yes it has and it is a great thing - hopefully no messages would be lost assuming that downtime is relatively short. This still does pose a (possibly minor) problem when some mails are urgent.

> f my local AT&T connection went down, it doesn't matter how open and resilient the Internet is, I'm not getting online until it's fixed.

Except that you could work from home, check your e-mail using mobile.

When this happens I just switch to tethering from my cell phone. Redundant enough.

I used to work for a relatively small dev-shop (9 persons) and we had two independent internet connections from two providers to avoid such problems. This was because done that way because there was only one fiber provider that wasn't really reliable (3+ hours downtimes every 1-2 months) and mobile tethering wasn't really an option as well because of nearby powerlines that made the reception quite a problem - to the point where our sales guy had to go outside the building during some calls. Luckily there was a second ISP - not really fast (10mbps was the best they could do) and quite expensive (we've paid more than twice more for that 10mbps than for a gigabit fiber), but still cheaper than having 9 people not able to work while waiting for the "main" ISP to solve their problems.