Users struggled to access the Online Postage Application on the Capgemini-run website for a number of hours yesterday morning.
This is the sixth consecutive month that users have experienced problems trying to access the Royal Mail's SmartStamp and online postage service since online data was migrated to new servers in December 2011.
But yet again, Royal Mail refused to provide any further details on what has been causing the glitches.
"Due to technical issues, some customers experienced difficulties accessing the Online Postage Application for a short period of time [yesterday] morning.
"The service has now been restored and we apologise to customers for any inconvenience this may have caused," a spokesperson for the company said.
According to messages on the social network Twitter, business customers trying to access their Online Business Accounts (OBA) were affected by the problems.
For example, when the Royal Mail customer services team posted on its Twitter feed that the technical issue had been resolved at 12.48 GMT, online bakery The Cake Nest replied to say:
"@RoyalMail i can now log on but still can't access OBA."