Latest update - 2018.05.26 - missing key on CentOS

[Nathan Christenson]

When trying to install the most recent update (packaged 2018.05.26) on CentOS7 I get the following message:
warning: /var/cache/yum/x86_64/7/Kolab_16/packages/roundcubemail-plugin-kolab_folders-assets-3.3.6-2.2.el7.kolab_16.noarch.rpm: Header V3 RSA/SHA1 Signature, key ID 0038d0db: NOKEY

I'm not sure where to find the key so that I can import it. Can anyone point me in the right direction?
Thank you!
Nathan
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