Does Posteo do a bunch of stuff that warrants a high rate for the higher end compared to the very affordable low end?
Posteo offers IMAP, CalDav, and CardDav. (Those were the features which sold me.) I think Tuta, and Proton don’t offer IMAP and none of them offer any WebDAV.
But does that relate to their storage pricing? Hard to say. Usually when I see things that are priced higher than what appears to be market rate, I understand that to mean the service provider doesn’t really want to do the thing. (Guaranteeing the availability of lots of GBs of storage for many users)
Yeah, maybe something like that. I switched to Posteo (from Proton, which didn’t have IMAP back then, and that from Gmail) like a decade ago. And something that I appreciate about it is that I’ve developed a practice/ habit of archiving or deleting old emails.
I save important photos, documents etc to my local disk and then delete the email. For context, I have 70 messages in my inbox.
Like I said above, the way I think about it is they don’t want the cost of guaranteeing additional storage, but it’s just a guess. If you were to send them an email and ask (I’ve sent a couple over the years, they respond to email), I’d be curious what their public response is.