In the specific case of webmail[1], I would offer hosted instances.
OTOH, a need to commercialize a FOSS-project is always a latent conflict of interest and I personally only reluctantly make such software part of my stack: I might end up with core devs moving to a proprietary fork full time and not enough other devs to "just fork it".
As to the usage of the word 'webmail', I'd say it's been in techno-parlance for a long time, masquerading as recommended DNS settings.
By 'long time', I mean at least since the mid-to-late 90s. I would often see the word -- not in regular writing, but in tutorials, all the time. Setting up a cPanel instance, for example, you would often be instructed to set up your MX records as 'mail.yourdomain.tld', and your CNAME as 'webmail.yourdomain.tld', just so you'd have something convenient to type in your browser.
OTOH, a need to commercialize a FOSS-project is always a latent conflict of interest and I personally only reluctantly make such software part of my stack: I might end up with core devs moving to a proprietary fork full time and not enough other devs to "just fork it".
[1] when did this even become a word?