The launch of Yahoo's new email domain, ymail.com, has been beset with login problems.
Yahoo has admitted it has was unable to deal with the number of people wanting to get new email addresses, leaving some unable to set up accounts at all.
Others who had initially managed to set up the accounts were later unable to access them and were told that they had been disabled due to violations of the terms of service.
Some have also complained that they have been unable to integrate their existing Yahoo Mail accounts with their new ymail accounts.
Disappointed surfers have been making their feelings known about the teething troubles in the official ymail blog.
"I was planning on using my new ymail address, but had barely had the chance to sign in once and read the introductory email sent by Yahoo before I could no longer access my account when I went to login the next day," one user wrote.
Another commented: "If you can't merge the old account information into the new account what good it is changing anything. I finally can get the address name I have tried to have for about 10 years, but it is not worth having it if I can not merge contact information between the old and new accounts."
Ryan Knight, community manager for Yahoo Mail, apologised for the registration problems, saying the number of existing Yahoo Mail users who wanted to sign up for new accounts "far exceeded what we had anticipated".
He added: "We've updated our systems to accommodate these registration behaviors, and will be reactivating all impacted accounts today."
www.yahoo.co.uk/ymail