STLS in POP3 does not seem to work

Maybe I misunderstand something, but:

in pop3server.xml I have:

<pop3server enabled="true">
<bind>0.0.0.0:110</bind>
<connectionBacklog>200</connectionBacklog>
<tls socketTLS="false" startTLS="true">
<keystore>file://conf/file.jks</keystore>
<secret>password</secret>
</tls>
<connectiontimeout>1200</connectiontimeout>
<connectionLimit> 0 </connectionLimit>
<connectionLimitPerIP> 0 </connectionLimitPerIP>
<handlerchain enableJmx="true">
<handler class="org.apache.james.pop3server.core.CoreCmdHandlerLoader"/>
</handlerchain>
</pop3server>

In smtpserver.xml I have identical tls section.

When I connect to pop3:

• CAPA command does not return anything about TLS,
• STLS command gives ERR
• STARTTLS command gives ERR.

To check if the keystore, password etc. are correct, I am checking against SMTP server, and:

• EHLO response includes 250-STARTTLS
• STARTTLS response is 220 2.0.0 Ready to start TLS

I do not see anything suspicious in the logs.