Telstra is under pressure over a sustained outage to its BigPond email service that has seen some customers unable to send or receive mail since just before 2pm AEST yesterday.

The telco briefly acknowledged the problems on its service status page and said it was "currently working on restoration activities". Similar acknowledgements were posted to Facebook and Twitter accounts.

A Telstra spokesperson told iTnews the issue was with three of its mail storage services, which required hardware replacement and an application rebuild.

It had recovered two of the servers just before 6pm last night which restored services to two-thirds of affected customers. The third server was restored at 8am this morning.

The spokesperson said customers may experience a small delay in getting all their messages as the servers process the backlog.

"We have queued our customers' emails during this outage and advise that as service restores and customers can connect again, they may not have all their latest emails immediately but they will be delivered over a short time," the spokesperson said.

Telstra's 4.2 million BigPond email mailboxes are underpinned by Microsoft's Windows Live cloud platform.

The outage comes after Telstra business customers were yesterday hit by a five-hour IP telephony disruption due to problems with Telstra’s primary IP Telephony (TIPT) server.