Thousands of email users are unable to send or collect messages this morning after a catastrophic server application crash at webmail host GMX.

Customers have been unable to access services for days. The company's online forum is filled with posts complaining about lack of access and the company's failure to communicate the problem to customers.

The company's advertisements promise "over 99 per cent guaranteed availability". No details have been made on whether the company plans to compensate customers for the outage.

A company representative said engineers were working to rectify the issue but could not confirm how long the work would take.

"We are confident that these measures will return the service in the coming days. We apologise unreservedly," he said.