Yes, quite frequently.
I run an opt-in village newsletter. It is quite common for all those who have @btinternet.com addresses to experience considerable delays in receiving the newsletters, usually of the order of 20 to 150 minutes.
I have complained to @btinternet.com on a number of occasions in the past three years - to no avail, so I don't complain anymore. BT's attitude is that I am not a BT customer so they won't deal with me, they have however admitted that they are aware of the problem, but point out that emails don't fail but are merely delayed!
I believe that the originating address may play a part, I have a couple of domains, plus addresses at Fastmail.Com & POBox.Com - emails sent from Fastmail.Com & POBox.Com appear to be less affected by the BT problems, BUT they can still be delayed.
A few of my users have moved from @btinternet.com & @btopenworld.com, and that seems to totally resolve the problem, so that's what I recommend to those who raise the issue with me.