Tiscali UK suffered an attack on its network on Tuesday, resulting in a loss of service for some users.
One reader got in touch early Tuesday afternoon, having been unable to access the ISP's POP3 email services or get through to its customer service call centre.
The precise nature of the attack is as yet unknown.
The company said in a statement: "Tiscali has been subject to an external attack on our network. However we have taken steps to identify the source and isolate the problem. Service has been restored for Tiscali customers accessing the portal and services through a Tiscali dial-up but the portal is currently unavailable to non-Tiscali subscribers."
It continues: "Customers can use Webmail, Outlook and browse the Internet but may be experiencing occasional delays in accessing the Tiscali portal. We have placed customer information on our status line and status board, the customer service team has been handling calls and our engineers are working to completely restore a normal level of service. Tiscali would like to apologise to any customers affected at this time."