Email traffic volumes are set to double within the next few months if the recent growth rate in spam messages continues, according to a warning issued by email management firm Email Systems.

While spam has been an ongoing problem for many years, Email Systems said the rate of growth in spam messages has suddenly accelerated since July 2006, leading to total email traffic growing by between 25 and 35 percent each month since then.

Businesses relying on local filtering to block spam and email-borne viruses may find their systems overwhelmed by the volume of incoming traffic, the company warned.

“With such an exponential rise in traffic since July, it is probable that many email users could be looking at a very severe downturn in speed of data provision if this trend continues at the current pace," said Neil Hammerton, chief executive of Email Systems.

Last year, internet service providers (ISPs) faced growing calls from businesses to do more to block spam before it reached customers.

Email Systems attributes the surging volume of junk emails to a change in tactics by the spammers. Single emails are no longer being distributed to a large number of recipients, but are instead being sent to smaller groups of addresses with subtle changes in content to evade detection by filters.