Yahoo Mail crashed earlier today for two hours, affecting people with BT and Sky email addresses as well as Yahoo accounts.
Yahoo is owned by US giant Verizon and provides the email platform which is used by several companies.
Undiagnosed problems left customers unable to access their accounts from around 11am until shortly after 1pm GMT and it has now been resolved.
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According to live outage detector site downdetector, 45 per cent of affected BT customers are having email access problems
Disgruntled customers took to Twitter to bemoan Yahoo Mail directly, with downdetector seeing a spike in complaints of up to 586 separate reports as of 11:56am GMT (pictured)
A BT spokesperson told MailOnline: ‘Yahoo experienced an issue for a short amount of time which means that some of our customers were unable to access their BT Yahoo email accounts.
‘Yahoo has now resolved the issue, we’re sorry for any inconvenience caused to our customers.’
Sky email custyomers took to Twitter to vent their frustration at being left without internet for several hours. It seems the issue started spontaneously around 11am, and was resolved shortly afterwards
While third-party apps seem to be failing, some BT customers claimed they were also experiencing problems with desktop computers (pictured)
Yahoo Mail crashed earlier today for two hours, affecting people with BT and Sky email addresses as well as Yahoo accounts
According to live outage detector site downdetector, 50 per cent of affected BT users experienced internet issues, but BT claims problems were limited to its email platform.
Around 45 per cent of BT complainants cited email access problems.
However, the vast majority of issues with Yahoo Mail were with logging in, amassing 82 per cent of all complaints.
Other issues were receiving and reading email messages, totalling 11 and five per cent, respectively.
Disgruntled customers also took to Twitter to bemoan Yahoo Mail directly, with downdetector seeing a spike in complaints of up to 586 separate reports as of 11:56am GMT.
But while third-party apps seem to be failing, some users claim they are experiencing problems with desktop computers.
MailOnline has approached BT and Yahoo for comment.
BT crashed for hundreds of users up and down the UK. The biggest broadband provider in the UK is experienced significant email connectivity issues
BT customers live outage map (pictured) reveals customers around the UK were struggling to access their accounts, with a focus in the south-east and London