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Didn’t they also include calendaring at some point?

Didn’t JZW once famously say all software grows until it eventually has an email client?

You're thinking of Mozilla Sunbird.

Netscape Communicator included a calendar at one point.

And Usenet! That never caught on either, though. We've had more web browsers with RSS support than web browsers with email support.

Opera was also a mail client and IRC client at one point.