It’s been bubbling around 75% to 80% for the year, but the last 60 to 90 days has been a barrage, said Scott Petry, chief technical officer of Postini Inc.

A surge in spam around the Thanksgiving holiday is not unusual. The so-called Black Friday post-Thanksgiving sales rush is roughly as important a period as the January sales are to UK retailers. Spammers, like any marketers, want to exploit consumers willingness to reach for the wallet.

We typically see a seasonal spike when we look at the fourth quarter across a number years, we see a lull in the summertime and an increase in the fall, but this is an unprecedented volume and it continues to increase, Petry said.

This time around a number of technological changes in how sophisticated spammers operate has meant yet another spike in volumes, even as it seemed like the problem was on the wane.

One possible reason spam filters are seeing more emails is that spammers have figured out a way to short circuit certain basic graylist filters, according to Petry.

One of the reasons you’re seeing a spike is seasonal, but it’s not related to the content of the spam itself but really the mechanisms used for sending the spam, he said.

Previously, spammers sent out huge volumes of email from computers that didn’t hang around to ensure the spam had been delivered. While a legitimate sending mail server may have stored undelivered mail in a deferral queue, spambots did not.

This lead to people configuring their mail servers to initially deny connections to computers on a graylist of suspicious IP addresses. If it was a spambot attempting the send, chances are that the spam would not arrive a second time.

But spammers have figured that out and adjusted their tactics accordingly, according to Petry. This year, they started resending emails to spoof the behavior of a legitimate deferral queue. Even if the spam still doesn’t reach its intended recipient, the number of spams being attempted rockets.

Postini saw a 59% increase in spam between September and November, and the number of attempted SMTP connections in October was up by 10 billion to a total of 39 billion.

But will it get better after Christmas? No, according to Petry.

We’ve never seen a material decrease in spam, although in the last year or so it’s flattened out somewhat, he said.