Google is to update Gmail with a behavioural advertising feature that it said will make ads that appear on the service "as relevant and useful as possible".
According to The Telegraph, the technology analyses messages and what the receiver does with them to build up a picture of their likes and dislikes.
The company said that with this system advertising would be based on "signals" such as what users receive the most email about, which emails they read and reply to, and the identity of their most regular contacts.
On the Gmail help page the company gives an example of how it sees the service working: "Using some of the same signals that help predict which messages are likely to be important to you, Gmail will better predict which ads may be useful to you. For example, if you’ve recently received a lot of messages about photography or cameras, a deal from a local camera store might be interesting. On the other hand if you’ve reported these messages as spam, you probably don’t want to see that deal."
In its post, the company said that a typical user could expect fewer ads as a result of the new system and stressed that no personally identifiable information is shared with advertisers. It also said that users would be able to opt out of the feature when it is introduced.