¡±I suspect this may be one for whoever runs?, but can they sort out their bulk email settings. Pretty much every time I get a digest from the <redacted> group I have to unbounce my account because their bulk email settings are dodgy and iCloud bounces it.
You or your member could forward the info to [email protected], not that I think that will do much good other than to reassure the member that Groups.io is on top of it. I've absolutely no doubt that they've seen that info before, many times over, and I know they track deliverability problems with each email service.
Groups.io's bulk email settings are not "dodgy", reading down iCloud's bullet list even I can tell that those bases are covered. The one thing that might have be confusing iCloud is that Groups.io is a mailing list service - so the From name and address won't be consistent for individual messages. But for digests it is always the group address, so that's not the problem in this member's case.
Groups.io also does not periodically remove inactive subscribers. But what does iCloud mean by "inactive", and how would they know?
In this case, I think your member needs to look to iCloud to solve the problem, or use a less problematic email service.