Telecoms company Eir says that some of its customers are continuing to experience problems accessing its webmail service.
The technical difficulties are also impacting the ability of users to contact the company's web chat team.
The issue appears to have begun yesterday and has led to users taking to social media to vent their frustration.
Eir says it is currently investigating the cause of the problem and hopes to have normal service resumed by later this evening or early tomorrow.
It has advised those effected to try clearing the cache on their web browser as this might assist.
The company has apologised for the inconvenience caused and has thanked customers for their patience.
Eir's Webmail service has around 200,000 regular email users, although the difficulties are not impacting all of them.
A spokesman said the issue was not caused by a hacking incident, but by a techical fault.
The company is not able to say when full-service will be restored.
Separately, the company said following today's adverse weather conditions during Storm Ali, 86 of its mobile phone mast sites are without power and as a result service in those areas is impacted.
This represents 4% of its total number of masts.