It means that for more than 30 days, you’ll be unable to send or receive emails that have to do with that email provider.

I’m not sure how you arrive at that. Whether you file a GDPR Art.77 complaint is independent of how you ultimately decide to reach the other party.

This is not what I would do but this is what most activists would do:

1. Use a residential dynamic IP address to attempt to send an email to a recipient whose data processor (email provider) is Microsoft.
2. Keep the logs of the MS server refusing you.
3. File an Art.77 GDPR complaint against MS.
4. In parallel, use a different webmail account to email your correspondent. Ideally wait a week or two after filing the GDPR complaint.

The fact that your webmail provider can reach MS does not obviate your Art.77 complaint.

Personally, I have indeed quit sending email. When I need to reach an MS recipient, I use fax or snail mail and I do not give them an email address, thus forcing them to respond by snail mail. Most people will not elevate ethics above convenience like that, but to each his own.

but not being able to receive them gets really problematic.

That’s a separate matter and it depends on what email address you supply. You can attempt to send from your own server using any email address you want, even an @gmail.com address if that’s your thing. The email address you share with the other party need not be one that associates to your mail server.

I personally do not even share an email address with MS users, so those users can only reach me by postal mail. But of course this move requires a higher level of discipline on your part.

Fighting for your rights… with gdpr, yeah, I’m sometimes doing it, but the problem is, sometimes tcompanies fail to respond … and if they take 30 days… or longer to give a response you’re really at a huge loss

Not sure what you mean by being at a huge loss. Filing a GDPR complaint is gratis, by law. It’s indeed typical that data controllers ignore complaints. After 30 days of ignoring your request, you have a sound case for an art.77 complaint. The DPA will also likely do nothing, but you’re not at a loss for complaining. If the DPA decides to simply contact the data controller, they will dance. The case will still go nowhere, but the data controller will respond to the DPAs inquiry, if they make one.