Damn, Tuesday morning and Gmail is still on the fritz. Problems started around Sunday lunchtime and the service has been intermittent since then.
(update 2 May 2020)
The link now takes you this page
Banned Content Warning The group you are attempting to view (Gmail down) has been identified as containing spam, malware, or other malicious content. Content in this group is now limited to view-only mode for those with access.
Group owners can request an appeal after they have taken steps to clean up potentially offensive content in the forum. For more information about content policies on Google Groups see our Help Center article on abuse and our Terms of Service.
I wonder what kind of “offensive content” we’re talking about here…