IT administrators are being hassled by disgruntled staff who have found themselves cut off from Gmail with little explanation.

Google reported yesterday evening that a "small number of customers" were having problems and that the situation would be resolved shortly. However, some IT administrators have reported outages of nearly 24 hours.

"I'm in Seattle and was wondering if anyone on the Pacific West Coast is still getting '502 Server Errors' when attempting to access some (or all) of your email hosted on Google Apps," one administrator wrote on the Google Apps message board.

"This outage has hit us pretty hard and we've been out of email for 24 hours and now business is suffering."

Another administrator wrote: "Since yesterday around 4pm my CEO cannot access his mail. He gets a 502 temporary error. I have to speak with the boss again and he's po'd. This is a mission critical issue here.

"Apparently Google mail is not very reliable. I think I would have pushed for something else before we switched if I had known the level of unreliability."

Gmail has been hit by an increasing number of outages, and this latest case will harm Google's attempts to tout itself as an online service for businesses.

Customers pay $50 a year for the full Google Apps business package and this includes a guarantee of 99.9 per cent reliability.

While no-one is suggesting that Google is approaching default on its service guarantees, the outage has angered many who are now relying on the service.

Google co-founder Sergey Brin claimed today that one million businesses are using Google Apps.

However, some observers have little sympathy with the administrators' plight. "Why are you not running your own mail server if email is that critical?" asked one poster. "Even my 16 year-old brother has his own."