Oracle 18c XE utl_mail: ORA-24247 although user and host are listet in ace

I had to upgrade our database from oracle 11g to oracle 18c XE. In 11g some scheduled jobs send emails to report database errors or report errors in the data. The user SYS ist able to send emails via the defined smtp_out_server but not the user which executes the procedures - although I granted the necessary privileges and produded an ace. This is the result of a query ob dba_host_aces:

HOST: 10.193.n.n | LOWER_PORT: 587 | UPPER_PORT: 587 | ACE_ORDER: 1 | GRANT_TYPE: GRANT | INVERTED_PRINCIPAL: NO    | PRINCIPAL: DBUSER | PRINCIPAL_TYPE: DATABASE  | PRIVILEGE: SMTP

I revoked and rebuild the ace, but nothing helps. If I try to send a mail via utl_mail with the DBUSER, I get ora-24247. It's a very simple test email:

BEGIN
   UTL_MAIL.send(sender     => 'chris@mailserver.de',
                 recipients => 'chris@mailserver.de',
                 subject    => 'UTL_MAIL Test',
                 message    => 'If you get this message it worked!');
END;
/

The same message/block sent with the user sys works.

Has anyone an idea what may be wrong or what I can check to solve this issue?

BR Christoph

I beg your pardon. The answer to my question is as simple as it could be. Our thrid party systems engineer told me this morning: "By the way. Did you get the email notifications work? I changed the smtp port ... Please use port 25 instead 587."

With port 25 it works.

Best regards Christoph