It has seemed to me for a while that they need to more fully compete with Google Workspace (formerly G Suite) and Microsoft Office 365. A big missing piece of that is email, as you said. They even acquired an email startup called Mailbox, but they killed it instead of adding an email service [1]. Every company needs email, and the most popular email services include Dropbox and Paper like products.
Slack is available as a standalone offering and is very popular, so a Slack clone may not be required. For everything else, limiting your customers to those already paying for duplicate services raises the bar. Your service needs to be enough better that it is worth paying for it twice.
Agreed. We have Office 365 because it was cheaper than hosted Exchange which we were using before. Dropbox needed email/collaboration tools (imagine Teams but years ago) - not dependencies on software that includes the same functionality.
Slack is available as a standalone offering and is very popular, so a Slack clone may not be required. For everything else, limiting your customers to those already paying for duplicate services raises the bar. Your service needs to be enough better that it is worth paying for it twice.
[1] https://www.theverge.com/2015/12/8/9873268/why-dropbox-mailb...