BT's email appears to have stopped working properly, with a flurry of users unable to see their messages.
The company's official Twitter feed apologised to affected customers and asked them to take a series of steps to try and get their inboxes working again.
There were a few reports of problems with BT phone and internet connections, but the vast majority of issues appeared to be related to email.
Users said that when they went to sign in through BT's webmail client, they were unable to login, despite apparently being connected and entering the right information.
The official BT account replied to affected users asking them to clear their cache and cookies before trying again, which seemed to fix the issue for at least some people.
Others reported that the issue appeared to resolve itself over the day.
Tracking site Down Detector showed a vast number of reports coming from all across the UK. While it indicated that there was also issues with internet service, that appeared to be the result of users who were complaining their email had broken being wrongly classified.