550 Invalid RDNS entry sending emails

I’m having an issue when sending mails to certain domains that check reverse DNS records.
My UCS server was configured using an internal domain name, then my hostname is server01.domain.local.
When sending emails it uses this FQDN, even when the public domain name is domain.com.ar.
And here is the issue, because for some email destinations I’m receiving the email in return stating that the email cannot be sent because of the RDNS record:

This is the mail system at host server01.domain.local.

I’m sorry to have to inform you that your message could not be delivered to
one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own
text from the attached returned message.

               The mail system

: host mail.destination.com[a.b.c.d] said: 550 Invalid
entry for e.f.g.h (in reply to RCPT TO command)

a.b.c.d is the public IP address of the destination email server and e.f.g.h is my public IP address. Our UCS server is behind a firewall, so e.f.g.h points to my public FQDN.
If I use a public page to check RDNS records, such as Misk, I see an output like this one:


1 hour PTR server01.domain.local
[Authoritative Nameservers]…

|# server01.domain.local|
|Forward Lookup Does Not Match Reverse Dns…|
|No A Records|
|[Authoritative Nameservers]…

I’m using UCS 5.
Any ideas about how can this issue be solved?
Thanks a lot in advance!
Best regards,


Does anybody have some idea about this issue?
Maybe changing the way Univention’s Postfix configuration is regarding how the mail server identifies to the world?
Today it identifies as server.domain.local, but this “domain.local” is internal…server.domain.com is publicly reachable. Does this sound logical?
Thanks, and best regards,


you may consider changing this UCR variable:

mail/smtp/helo/name: <empty>
 This variable allows the configuration of the hostname the server used for identification as part of the SMTP protocol (EHLO/HELO). If the variable is unset, the fully qualified hostname is used


Hi Dirk!
I understand this is the perfect solution!
Thanks a lot!!!
Best regards,