Yahoo Mail, one of the largest web-based email services in the world, has been up and down Thursday for many of its 250 million users.

The company said in a statement:

Yahoo! Mail is currently inaccessible to some users. We are working to correct the issue and restore all functionality immediately. We know that this may have caused some inconvenience and we apologize to our users who might be affected.

Yahoo mail users took to twitter with the hashtag #yahoomail to express their displeasure, commiserate, or offer solutions. User e_warren wrote: I guess I should be honored - #yahoomail is only down for "selected users." I'm special!. While @bmorisette posted: My Yahoo Plus account has not had a problem all day - guess my $20 / year went towards better servers for paying customers #yahoo #yahoomail. 

Theories abound that Yahoo Mail's recent upgrade of its service and redesign is at fault. Others have pointed out that Yahoo's mobile site is still functional and is a good alternative until the service gets online.

Gmail, Google's email service, has had several notable outages in the past few years. There are conflicting numbers, but Yahoo is generally regarded to be the largest email service in the world.

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Reach Tom Dotan, not at his Yahoo address, here