Just host your own mail server and you can have as many accounts you want - I have more than a thousand since I use special addresses when communicating with anyone who is not friend or family. If you worry over reliability - which in my experience is not a problem to be worried over given the tenacity of SMTP in attempting to deliver messages to temporarily off-lined hosts - you could arrange a reciprocal agreement with someone you trust to host a backup (MX) server for your domain(s). You won't have to deal with commercial plans, virtue signalling, filtering, bankruptcies (other than your own) or any of the other bothersome irritants which can be encountered when dealing with commercial entities. People will tell you it is impossible to host your own mail, that it takes enormous investments in time, that you'll be inundated in spam, that your outgoing mail will not be accepted by the likes of Google and Microsoft and more dire warnings of mayhem and misfortune for those who do not pay someone else to do this work for them. Nearly all of this is untrue, hosting a mail server is no black magic. Just make sure to configure the thing correctly, using a smart host to take care of outgoing mail - this is most likely mandated by your IAP - and DKIM/SPF/... to please those hosts which require it. Use Spamassassin and (optionally) greylistd for spam filtering, this will take care of the spam problem. All of this can be run on a SBC like a Raspberry Pi.

Source: I've hosted my own mail for more than 25 years now, taking it with me from ISP to IAP, from country to country, even through a period where I only had dialup (the consequence of moving to the countryside - now I have gigabit fibre in the same location) by having an arrangement with a friend who ran backup MX for me. Linux + Exim + Spamassassin + greylistd + Dovecot + Sieve is all it takes, all of it is free, running a Raspberry Pi (or similar) costs a pittance. An additional advantage is that you'll be ready for the decentralised future of the 'net.