I've raised an issue on the email-ext plugin.
http://issues.hudson-ci.org/browse/HUDSON-7402
SauravSengupta wrote
There seems to be some interaction between these two plugins. I'm using the timestamper plugin to add timestamps to the build logs. I'm also using the build log regex functionality in the email-ext plugin to add the relevant section of the logs to the email. But if the build logs have timestamps in them, I see a lot of garbage (possibly Unicode?) in the email.