If the SMTP host needs authentication, you can provide your <username> and <password> in the <configuration> section:
<project>
...
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-changes-plugin</artifactId>
<version>2.3</version>
<configuration>
<smtpHost>mail.yourhost.com</smtpHost>
<smtpPort implementation="java.lang.Integer">25</smtpPort>
<username>some@email.com</username>
<password>somepassword</password>
...
</configuration>
</plugin>
</plugins>
</build>
...
</project>