I'm sure as a huge company you have thought this through in detail and know what you have done.
Removing these features from the free tier has basically crippled the service.
Fair enough you made no money out of these accounts so some will say I have no right to complain.
But here is my complaint anyway.
By removing those key features you have turned it into needing paid accounts for all but the most trivial purposes.
For clients I set up a webmaster@ account that forwards technical emails to myself.
Then I set up forms@ for the contact form to use which just forwards the emails on to the clients account. This protects them from breaking the website when they change their email login.
Then I set up the clients accounts.
If any one account needs to be upgrade to function beyond this new crippled "free" tier then every account needs to be converted to a paid account, so you have basically cancelled your free service no matter what you may pretend.
I guess you have built up the user base to levels that you wanted now and the free users are not converting to paid users fast enough.
You should have at least done this as a staged changeover with some kind of communication of your intentions. The client I was setting this account up for was expecting to get this service free and now their first experience of the Zoho brand is going to be a negative one. I could have managed expectations better if I knew what the situation was going to be.
Thank you for your free services over the years but not thank you for this abrupt transition and your poor monetisation model. Giving 50 accounts was too many for all of my clients. I don't know if anyone cares about it being ad-free. Forcing every account to go paid just to upgrade one just forced us to create "archive" accounts to store the gb in. I have converted 1 client out of about 25 into a paid user because you didn't set it up right to sell.
3-5 email accounts on the free tier would be enough. A small amount of storage. Imap and forwarding included. Letting people upgrade individual accounts. This way most of my clients would have ended up giving you some money and they would have done it happily because they would have had their free service and be happy to pay a small increment to solve a business problem.
But what I have now is basically me having to pitch you head to head with Google and Microsoft and apart from the small saving with the tiniest tier I don't think you can boast superiority. Your support tickets are normally 3-5 days min. IMAP regularly times out. You messed with the email and introduced stupid smart filters which hid peoples emails. Your webmail client is alright but not top class. You roll features out that are half completed like this migration to a different way of doing dkim which has been ongoing for months. Now you have lost the hook to get people in and turn a blind eye to these issues.