We were assured, by Clapper and the NSA's defenders, that only
metadata was being collected on American citizens (for example, "Sally Smith sent an email from IP Address 123.45.678.9 at 11:53:08 p.m. on June 12, 2014, to edjones@acme.cz"

. We now know that is
not true. We now know that the NSA would save the content of the email, and any attachments -- for example the lingerie photo Sally thought only Ed would see. And we know that this "private" communication and attachment(s) could be, and was, accessed by a
low-level contractor.
"You can't know which emails to collect until you know which emails to collect." The NSA says that the precedent set by
Smith v. Maryland gives them the right to collect
all Americans' emails (and, presumably, to record all phone calls). To quote
Randy Barnett of Georgetown U.:
The paradigm of what the Fourth Amendment prohibited as “unreasonable” in its first sentence was the use of general warrants, which is why its second sentence requires that warrants must be particular. And, as USD law professor Donald Dripps
has shown, the seizure of papers for later search for evidence of criminal conduct was the epitome of an unreasonable search and seizure that was closely akin to general warrants. -
Washington Post, April 28, 2014
So, which emails to collect? When it comes to Americans' emails: Legally, constitutionally, the ones you have a
warrant to collect. Not
all the emails you might potentially need some day in the course of an unforeseen investigation.
And if my granddaughter's bathtub photo is among the data collected and stored, it's cold comfort to reflect that the NSA's data banks (purportedly) include only a fraction of a percent of all communications.