Believe it or not, it is a lot more complicated than you'd think for a single organisation to send tens of thousands of emails over a short period of time. ISPs and companies like Google that provide free email accounts have all sorts of protection in place to try to prevent and limit the amount of spam reaching their servers and people's inboxes, and that can end up with false positive spam identification.

Many of the delayed receipt of emails could be nothing to do with when BA sent them out.