First, choosing which communications links, or bearers, to access: GCHQ’s systems operate on a very small percentage of the bearers that make up the internet.
Then, selecting which communications to collect from those links that are being accessed: GCHQ applies levels of filtering and selection such that only a fraction of the material on those bearers is collected.
Finally, deciding which of the communications collected should be read: further targeted searches, ensuring that only those items believed to be of the highest intelligence value are ever presented for analysts to examine.
Only a very tiny percentage of those collected are ever seen by human eyes.
Given the extent of targeting and filtering involved, it is evident that while GCHQ’s bulk interception capability may involve large numbers of emails, it does not equate to blanket surveillance, nor does it equate to indiscriminate surveillance.