I'm one of the people affected by the iCloud Mail outage. On the other hand, I've been with Apple since 1984 and specifically has used dotMac, MobileMe and now iCloud.
Because of that long history, I long ago came to the conclusion never to reply on Apple's supplied email as either your only email account or else it if's mission-critical email--such as the main contact address for a business.
About 14 years ago I purchased a domain name (based on my family's surname) stictly for email use. It's linked to a plain POP3 account from Network Solutions. It's been completely reliable during that time. My address associated with that domain name as always been my primary email address. However, iCloud IMAP is nice. When things are working, I've got my POP3 account set to automatically foward all mail to my iCloud account. When iCloud is not working, I turn off forwarding--like I did yesterday. My mistake yesterday was to wait too long to turn off the forwarding, thinking that iCloud email problems would be short-term.
I always send important email via my POP3 account so that the address associated with that account is the one that's in the outside world. I also have a rule set up to sweep sent email from my POP3 account to my iCloud account so that those sent messages are available on all of my devices.
Yes, it costs a small amount to keep my domain name each year and it costs another small amount for the POP3 accounts for my wife and I. But I do like iCloud syncing and do like the IMAP email that's always available on all of my Apple devices. I think this setup works pretty well. Every time I think about canceling my POP3 account, something like this happens.
Don't flame me. There are many messages in the various threads in this forum describing situations where someone's iCloud mail is not working and that email account is critical for that person. There are obviously other approaches, including canceling iCloud. My approach is just one of many.