Problem receiving emails from noreply@forum.infinityfree.com

This sounds like a problem you’d need to raise with your mail provider.

End of the day, its your email provider that are rejecting the email, not InfinityFree.

It COULD be that the SPF, DKIM and DMARC records need updating. But that’s unlikely.

As for previewing your post, there’s a button top left of the editor that looks like this: or

If you click that, it’ll change between markdown and rich text mode. In Markdown, you get the preview panel to the right. (Or below on mobile)