Cela vient du certificat SSL qui est HS :

zimbra@zimbra:~$ /opt/zimbra/bin/zmcertmgr viewdeployedcrt

• ldap: /opt/zimbra/conf/slapd.crt
  notBefore=Nov 24 21:41:40 2016 GMT
  notAfter=Nov 24 21:41:40 2017 GMT
  subject= /OU=Zimbra Collaboration Server/CN=zimbra.xxx
  issuer= /O=CA/OU=Zimbra Collaboration Server/CN=zimbra.xxx
  SubjectAltName=zimbra.xxx
• mailboxd: /opt/zimbra/mailboxd/etc/mailboxd.pem
  notBefore=Nov 24 21:41:40 2016 GMT
  notAfter=Nov 24 21:41:40 2017 GMT
  subject= /OU=Zimbra Collaboration Server/CN=zimbra.xxx
  issuer= /O=CA/OU=Zimbra Collaboration Server/CN=zimbra.xxx
  SubjectAltName=zimbra.xxx
• mta: /opt/zimbra/conf/smtpd.crt
  notBefore=Nov 24 21:41:40 2016 GMT
  notAfter=Nov 24 21:41:40 2017 GMT
  subject= /OU=Zimbra Collaboration Server/CN=zimbra.xxx
  issuer= /O=CA/OU=Zimbra Collaboration Server/CN=zimbra.xxx
  SubjectAltName=zimbra.xxx
• proxy: /opt/zimbra/conf/nginx.crt
  notBefore=Nov 24 21:41:40 2016 GMT
  notAfter=Nov 24 21:41:40 2017 GMT
  subject= /OU=Zimbra Collaboration Server/CN=zimbra.xxx
  issuer= /O=CA/OU=Zimbra Collaboration Server/CN=zimbra.xxx
  SubjectAltName=zimbra.xxx

voici la procédure pour le régénérer:

https://wiki.zimbra....rtificate_Tools
https://wiki.zimbra....-_Single-Server
Single-Node Self-Signed Certificate

1. Begin by generating a new Certificate Authority (CA).
   /opt/zimbra/bin/zmcertmgr createca -new

2. Then generate a certificate signed by the CA that expires in 1825 days.
   /opt/zimbra/bin/zmcertmgr createcrt -new -days 1825

3. Next deploy the certificate.
   /opt/zimbra/bin/zmcertmgr deploycrt self

4. Next deploy the CA.
   /opt/zimbra/bin/zmcertmgr deployca