Nov 11 19:02:57 soporte postfix/smtp[4473]: warning: no MX host for signe.es has a valid address record
Nov 11 19:02:57 soporte postfix/smtp[4473]: BBDD64837B: to=<soporte@signe.es>, relay=none, delay=0.01, delays=0.01/0/0/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=zmail2.signe.es type=A: Host not found)

I seems that the SMTP server, zmail2.signe.es, that the OTRS system is attempting to send email to does not exist (Host not Found). As your system logged stated a few lines earlier there was no valid MX host for the domain.

When I look up MX records for signe.es I get a different response that you have here. I'd look at your DNS settings and verify that they are functioning correctly/accurately.

I would say my Spanish is worse than your English.