I'm not saying that the alternatives are better than email (e.g. at my job, Slack has replaced email for communication, and Gitlab/JIRA/Confluence/GoogleDocs is used for everything that needs to persist). The focus has shifted away from email for communication (for better or worse).
A point that I don’t think is being appreciated here is that email is still fundamental to communication between organizations, even if they are using something less formal internally.
One’s nephew might not interact in a professional capacity with other organizations, but many do.
B2C uses texting. Even if B uses email, C doesn't read it. And that is becoming just links to a webapp.
B2B probably still uses email, but that's terrible because of the phishing threat. Professional communication should use webapps plus notification pings which can be app notifications, emails, or SMS.
People to people at different organizations again fall back to texting as an informal channel.
I don’t doubt that vendors in some industries communicate with customers via Slack. I know of a few in the tech industry. The overwhelming majority of vendor and customer professional communication happens over email.
