Exactly. No way does it take 50 people to scales mattermost to 5k because of smtp. This op made that all up.

I think you are really underestimating the bureaucratic overheads in a large company. It is not the same as a 3-person startup serving 5000 customers. Of course I pulled that number out of the air, but the point is that it can make sense. I think I am right around the ballpark of needing a 5 people team to serve 500 users - you'd need a minimum of 3 people just to make sure there is enough redundancy if one person is sick or goes on vacation. You'd need 24x7 on-calls. The scaling factor probably changes after that - may be it is 10 people for 5000 users instead of 50.

Adding to other large company problems, these people will need management layers, the team will need a charter for growth. Who wants to be the maintainer of the Mattermost servers in a large company? Add all of this up and then the slack deal starts to look reasonable.

Edit: Just to add some real numbers, slack costs $12.50 per user per month [1] - that is ~$750k per year for 5000 users = 5 engineers. (More like 3 really in the Bay area)

[1] https://slack.com/pricing

Your general point is solid, but one quibble with the numbers - even the pricing page has an "enterprise" tier "for very large businesses".

There's no way a company with 5000 Slack users is paying the sticker price per head - they'll call Slack's enterprise sales team and negotiate some volume discount with whatever shiny enterprise-grade features, SLAs, support guarantees, etc. they need.

Or you have your existing corporate IT team manage it the same way they're managing other internal apps.

There's no way it suddenly needs a new team of dedicated full time resources.

This is a more realistic scenario. I own/operate shared services for thousands of users on a team of 3.

If it takes you that many engineers you are either using the wrong software or using it incorrectly.

At Uber scale, you probably already have your own SMTP servers used by all your employees, so that's not really a problem.

Moreover, email is hard and does require a dedicated team, but the order of magnitude is wrong here. 5 people is plenty.