With apple you’re limited to 5 sending addresses per domain, so no I cannot reply as the from address to most, but that hasn’t been an issue for me at all.

Depends on your use case. I went with using a custom domain with my iCloud mail account. This lets me accept all messages sent to my custom domain.

So when I create accounts I just use that as the email address like this: lemmy@customDomain.com, bsky@customDomain.com, etc.

They all go to one mailbox but that’s all I need anyway. I’ve been happy with it.