Internet and tolls vendor Slingshot is the latest ISP to add filtering abilities to its email services.
Industry figures show that one in 200 emails typically contains a virus, Callander says, and spam accounts for 30% of email traffic.
The service was launched yesterday. Slingshot is offering antivirus or antispam filtering for $2.50 a month, or both for $4 a month.
The company is trialling an ADSL service, which will be rolled out in the next few weeks, Callander says.