> Also, wouldn't your reasoning allow the government to avoid any allegations of 4th amendment violations by pointing to the NSA computer that does the actual scanning?

That's assuming the scanning never results in any information being conveyed to a person or recorded anywhere someone might eventually read it. That wouldn't provide much use to the government.

> None of that is true for many types of digital information held by third parties.

That depends on the third party. Not all email providers do that. And if scanning your email to target advertising was the determinant of whether the government could read it without a warrant, email providers would stop doing that or people would stop using them.

And then wouldn't it change based on whether the scanning is done client side or server side?

> Arguably, most clear-text online traffic falls in the latter bucket.

That puts a different spin on the whole encryption debate. If not encrypting traffic allows the government to read it without a warrant, a government encryption ban takes on a whole new meaning.

And the traffic increasingly is encrypted. Hosts are increasingly using TLS for HTTP and SMTP.