Comment by kenmacd

Not sure on the reputation, but I personally haven't had any issues emailing people using gmail or microsoft. They have a good DNS Diagnostics page that checks all your domains DKIM/SPF/DMARC settings.

I've been using identities created in the admin panel, but they do have subdomain addresses where everything to *@user.domain goes to user@domain, and you can configure a 'Catchall' address (and of course 'plus addresses'). I haven't used either though.