Research in Motion is still investigating why BlackBerry users throughout North America couldn't access their e-mail yesterday morning.

Bloomberg reported that the outage affected BlackBerry phones on all four US. wireless carriers. Canada's largest carrier, Rogers, also confirmed the interruption. The outage only hit e-mail, leaving Internet and text messaging unaffected.

RIM uses an Internet-based service to push e-mails to the handheld without going through an enterprise server. This appears to be the root of the problem, as corporate users didn't experience the same delays as consumers.

RIM has yet to explain what went wrong, but previous outages may reveal clues. In 2007, RIM blamed one lengthy service interruption on a new software routine.

This routine was supposed to optimise system cache memory, but instead caused an e-mail outage that lasted at least 12 hours. RIM said its back-up system proved to be inadequate as well.

Last year, another e-mail outage lasted for a several hours. RIM said it ran into problems while upgrading the capacity of its infrastructure in order to satisfy demand.

Previous upgrades had gone off without incident, but perhaps this is just another case of growing pains for the smartphone maker as it tries to accommodate more consumers.