Virgin Media's Webmail customers have been hit by service difficulties since Friday, specifically those on ntlworld.com, blueyonder.co.uk and virginmedia.com email addresses.
The provider has been suffering from a number of technical and SPAM problems since it began moving customers from Gmail platforms to the new semi-in-house system.
Google pulled out of offering Gmail support for ISPs earlier this year, causing many companies, including Virgin, to take their systems in-house.
The latest issue has posed intermittent problems for customers trying to access Virgin's Webmail and IMAP system.
Having initially claimed on Saturday that the latest problem had been fixed, ISPreview reported it was still affecting customers yesterday evening (November 16th).
An update from Virgin at the time read: "It appears this issue is still ongoing.
"Our sincere apologies for any inconvenience this is causing. Our engineers are continuing to work hard to get this resolved as soon as possible."