A US security vendor claims to have discovered the reason for Yahoo’s alleged poor email delivery: as many as half of its email hosts can be "closed" at any one time.

According to trimMail's Email Battles site, which recently monitored 16 of the company's advertised email hosts 240 times over a half-hour period, only 133 of its probes were answered. Many of the servers were closed and unavailable.

Overall availability ranged from 25 to 75 percent over the admittedly short test period. The average availability was 55 percent, with the worst of the servers available only seven percent of the time.

The measurements were taken using the company's freely available web tool Mail Server Profiler.

Yahoo struggles with a reputation for mediocre service in some quarters, but it is difficult to know what to make of these figures. The company is likely to counter that its accusers took the readings over a short and untypical period, or that the hosts being closed was not in itself indicative of service levels.

The site suggests paying customers take their business elsewhere rather than waste their own server resources trying to cope with mail resends.

In a single-query repeat of the Email Battles test, Techworld discovered that six of the 16 mail hosts were marked as closed – a similar result. By comparison, of the 16 possible hosts on Hotmail, four were found to be closed, while all of Gmail’s eight hosts were up.

It is impossible to say whether this comparison is typical or not, or that the fact that the hosts are closed is in itself the reason for service levels – that would require a much longer test. It would also be dependent on traffic volumes at a given moment in time, which can vary.

Yahoo was not available for comment at the time of going to press.

This story first appeared on Techworld.com.