Jenkins email-ext plugin fails to send email, the error is

Failed to create e-mail address for _developer1@xxx.net_
Failed to create e-mail address for _developer2@xxx.net_
Failed to create e-mail address for _developer1@xxx.net_
Failed to create e-mail address for _developer1@xxx.net_

(Names and domain are changed)

Jan 13, 2013 7:15:56 PM hudson.plugins.emailext.ExtendedEmailPublisher addAddressesFromRecipientList
WARNING: Could not create email address.
javax.mail.internet.AddressException: Domain contains illegal character in string ``_developer1@xxx.net_''
at javax.mail.internet.InternetAddress.checkAddress(InternetAddress.java:1269)
at javax.mail.internet.InternetAddress.parse(InternetAddress.java:1091)
at javax.mail.internet.InternetAddress.parse(InternetAddress.java:633)
at javax.mail.internet.InternetAddress.<init>(InternetAddress.java:111)
at hudson.plugins.emailext.EmailRecipientUtils.convertRecipientString(EmailRecipientUtils.java:60)
at hudson.plugins.emailext.ExtendedEmailPublisher.addAddressesFromRecipientList(ExtendedEmailPublisher.java:687)
at hudson.plugins.emailext.ExtendedEmailPublisher.createMail(ExtendedEmailPublisher.java:508)
at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:297)
at hudson.plugins.emailext.ExtendedEmailPublisher._perform(ExtendedEmailPublisher.java:289)
at hudson.plugins.emailext.ExtendedEmailPublisher.perform(ExtendedEmailPublisher.java:249)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:810)
at hudson.model.AbstractBuild$AbstractBuildExecution.perJan 13, 2013 7:15:56 PM hudson.plugins.emailext.ExtendedEmailPublisher addAddressesFromRecipientList
WARNING: Could not create email address.
javax.mail.internet.AddressException: Domain contains illegal character in string ``_developer1@xxx.net_''
at javax.mail.internet.InternetAddress.checkAddress(InternetAddress.java:1269)
at javax.mail.internet.InternetAddress.parse(InternetAddress.java:1091)
at javax.mail.internet.InternetAddress.parse(InternetAddress.java:633)
at javax.mail.internet.InternetAddress.<init>(InternetAddress.java:111)
at hudson.plugins.emailext.EmailRecipientUtils.convertRecipientString(EmailRecipientUtils.java:60)
at hudson.plugins.emailext.ExtendedEmailPublisher.addAddressesFromRecipientList(ExtendedEmailPublisher.java:687)
at hudson.plugins.emailext.ExtendedEmailPublisher.createMail(ExtendedEmailPublisher.java:508)
at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:297)
at hudson.plugins.emailext.ExtendedEmailPublisher._perform(ExtendedEmailPublisher.java:289)
at hudson.plugins.emailext.ExtendedEmailPublisher.perform(ExtendedEmailPublisher.java:249)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:810)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:785)
at hudson.model.Build$BuildExecution.cleanUp(Build.java:192)
at hudson.model.Run.execute(Run.java:1587)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:236)formAllBuildSteps(AbstractBuild.java:785)
at hudson.model.Build$BuildExecution.cleanUp(Build.java:192)
at hudson.model.Run.execute(Run.java:1587)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:236)

First I thought is the problem is in email-ext plugin, but when I went to "Changes" tab and opened the page

http://host/jenkins/user/Developer%201%20__developer1@xxx.net_/
(hostname changed)

it showed

Jenkins User Id: Developer 1 _developer1@xxx.net_

For unknown reason Jenkins adds a leading and trailing underscore to email address

Environment
Jenkins ver. 1.498
Jenkins Mercurial plugin 1.42
Jenkins Email Extension Plugin 2.25
Mercurial Distributed SCM (version 1.4.3)
Ubuntu 10.04.4 LTS
Java(TM) SE Runtime Environment (build 1.6.0_32-b05)
Java HotSpot(TM) 64-Bit Server VM (build 20.7-b02, mixed mode)

We have a build cluster with a master and two slaves, this problem happened on the slave machine.

When I type hg log on Jenkins job's workspace, then all changesets have
correct email address without underscores, so it is not Mercurial configuration problem.