You need to add some extensions (wagon-scm, maven-scm-manager-plexus and the maven-scm-provider for your SCM system, see examples below) to your pom and use URLs in the SCM format.
Add the following extensions to your pom and use a wagon-scm url in the distributionManagement site url.
<build>
<extensions>
<extension>
<groupId>org.apache.maven.wagon</groupId>
<artifactId>wagon-scm</artifactId>
<version>1.0-alpha-7-SNAPSHOT</version>
</extension>
<extension>
<groupId>org.apache.maven.scm</groupId>
<artifactId>maven-scm-manager-plexus</artifactId>
<version>1.0-beta-3-SNAPSHOT</version>
</extension>
<extension>
<groupId>org.apache.maven.scm</groupId>
<artifactId>maven-scm-provider-svnexe</artifactId>
<version>1.0-beta-3-SNAPSHOT</version>
</extension>
</extensions>
</build>
<distributionManagement>
<site>
<id>my.svn.server</id>
<url>scm:svn:https://username@svn.apache.org/svn/root/module</url>
</site>
</distributionManagement>Same as before, but changing svnexe to cvsexe and using a CVS svn url.
<build>
<extensions>
<extension>
<groupId>org.apache.maven.wagon</groupId>
<artifactId>wagon-scm</artifactId>
<version>1.0-alpha-7-SNAPSHOT</version>
</extension>
<extension>
<groupId>org.apache.maven.scm</groupId>
<artifactId>maven-scm-manager-plexus</artifactId>
<version>1.0-beta-3-SNAPSHOT</version>
</extension>
<extension>
<groupId>org.apache.maven.scm</groupId>
<artifactId>maven-scm-provider-cvsexe</artifactId>
<version>1.0-beta-3-SNAPSHOT</version>
</extension>
</extensions>
</build>
<distributionManagement>
<site>
<id>my.cvs.server</id>
<url>scm:cvs:ext:username@cvs.apache.org:/cvs/root:module</url>
</site>
</distributionManagement>