Tens of millions of BlackBerry users in Europe, the Middle East and Africa have been unable to receive or send emails and messages through their phones, following an outage at the server systems of parent company Research In Motion (RIM) in Slough, Berkshire.

The outage, which occurred at about 11am BST on Monday, was still affecting users more than four hours later with no time given for when it was expected to be resolved.

The company released a brief acknowledgement of the problem at 3.30pm, saying: "We are working to resolve an issue currently impacting some BlackBerry subscribers in Europe, the Middle East and Africa. We're investigating, and we apologise to our customers for any inconvenience caused while this is resolved."

BlackBerry systems receive and send emails and BlackBerry Messenger (BBM) communications via encrypted connections to RIM servers located around the world. The systems are particularly popular in a number of Middle East countries where they allow secure communication that the government cannot tap. RIM has come into conflict with a number of governments around the world, which have demanded oversight of email and BBM messages.

The failure will be a huge embarrassment for the company, which has been successful in building up its user base in the so-called "EMEA" (Europe, Middle East, Africa) region even while it has been losing users in North America.

At the end of August, RIM claimed that it had more than 70 million subscribers around the world. In July it claimed to have added 1 million subscribers in the EMEA region in less than three weeks. It would certainly have more than 10 million users in the total region.

The cause of the outage is not known, but one former RIM employee has told the Guardian that RIM has been ignoring problems with its server architecture that could prove its downfall for years. "They didn't start looking at scalability until about 2007, when they had around 8m active devices," the former employee said: "The attitude was, 'We're going to grow and grow but making sure our infrastructure can support it isn't a priority.' They have their own clunky infrastructure to do something that you don't really need a clunky infrastructure to do anymore."

The dramatic growth in the number of subscribers worldwide – nearly tenfold since 2007 – will have put serious strain on RIM's servers if such scalability has not been addressed urgently.

That's sad 

Just realising how virtually useless my phone is without my bis luks more like a calculator

this is so sad i feel like crying i am sure my boss will love this