Yes, this happens. Although I've been using SG for something like 10 years now and it's rare when a website blocks @SG (and the dozen other synonym domains) addresses.
What's nice with SG is that the emails are sent to /dev/null once the count is over whereas with a catchall, you keep receiving everything sent to any address for ever.
> with a catchall, you keep receiving everything sent to any address for ever.
That's true, and I wish Fastmail had a better way of managing rules remotely (with something like remote sieve or an API) so I could script a click-button-turf-address-forever. On the other hand, I don't mind still getting the follow-ups for some stuff. For example, Target has target@thatdomain.italkedabout.example for years to use for order confirmations.
You can also set a SG address to always forward emails coming from a particular email. So you could set it so that orders@target.com is always forwarded and doesn’t change the count and you’ll always get these but not the newsletter.
What's nice with SG is that the emails are sent to /dev/null once the count is over whereas with a catchall, you keep receiving everything sent to any address for ever.