There are ways of finding out if you've won anything in the monthly Premium Bond draw
- the app
- the website https://www.nsandi.com/prize-checker
This month (Sept 2020), the e-mail
was sent: Thu, 03 Sep 2020 05:32:20
was received: Sat, 05 Sep 2020 05:29:59
Pretty close to 48 hours.
I check two NS&I accounts with Premium Bonds that both got prizes and e-mails (separate e-mail addresses) this month, and both had the same timings (one arrived an hour later than the other).
The e-mail headers suggest it was held at mta6589.mxmfb.com
Received: from mta6589.mxmfb.com ([109.68.65.89])
by [servername deleted].co.uk with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
(Exim)
(envelope-from <bounce-[numeric deleted]-live@email.nsandi.com>)
id 1kEPpv-000Mu5-NM
for [e-mail address deleted]; Sat, 05 Sep 2020 05:29:59 +0100
Frankly, 48 hours is worse than useless (esp given the other channels are instant). NS&I may as well dump e-mail alerts unles they're going to make them a bit quicker.