I did read the howto

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[root@mail2 ~]# db yum_repositories set sogo repository BaseURL '
http://packages.inverse.ca/SOGo/nightly/5/rhel/$releasever/$basearch' EnableGroups yes GPGCheck no Name 'Inverse Sogo5 Repository' Visible yes status disabled
[root@mail2 ~]# signal-event yum-modify
[root@mail2 ~]# yum install smeserver-extrarepositories-epel -y
Loaded plugins: fastestmirror, post-transaction-actions, priorities, smeserver
Loading mirror speeds from cached hostfile
* base: mirror.freethought-internet.co.uk
* smeaddons: mirrors.misouk.com
* smeextras: mirrors.misouk.com
* smeos: mirrors.misouk.com
* smeupdates: mirrors.misouk.com
* updates: mirror.freethought-internet.co.uk
Package smeserver-extrarepositories-epel-0.1-40.noarch already installed and latest version
Nothing to do
[root@mail2 ~]# yum install smeserver-sogo --enablerepo=sogo,epel,smecontribs -y
Loaded plugins: fastestmirror, post-transaction-actions, priorities, smeserver
Loading mirror speeds from cached hostfile
* base: mirror.freethought-internet.co.uk
* epel: mirrors.ukfast.co.uk
* smeaddons: mirrors.misouk.com
* smecontribs: mirrors.misouk.com
* smeextras: mirrors.misouk.com
* smeos: mirrors.misouk.com
* smeupdates: mirrors.misouk.com
* updates: mirror.freethought-internet.co.uk
epel | 4.7 kB 00:00:00
smecontribs | 3.1 kB 00:00:00
sogo | 2.9 kB 00:00:00
503 packages excluded due to repository priority protections
No package smeserver-sogo available.
Error: Nothing to do
[root@mail2 ~]# yum update --enablerepo=sogo
Loaded plugins: fastestmirror, post-transaction-actions, priorities, smeserver
Loading mirror speeds from cached hostfile
* base: mirror.freethought-internet.co.uk
* smeaddons: mirrors.misouk.com
* smeextras: mirrors.misouk.com
* smeos: mirrors.misouk.com
* smeupdates: mirrors.misouk.com
* updates: mirror.freethought-internet.co.uk
No packages marked for update