I can't find a guide for this (they are old and don't work) and I can't seem to manage to install it. I can't install Postfix because of its dependencies, so I'm going with Exim, which I installed through yum install exim and it was the latest version. However, I have no idea where to go from here. I know that I need to install Dovecot or Cyrus and I want to install Horde (not Squirrelmail). Not to mention that I also want to keep MariaDB 10, which I installed from its repository, as well as PHP 5.5. I don't know where to go from here.
How do I install Exim and Horde on Centos 7 with MariaDB 10?
centos;email;dovecot;exim;mariadb
Dovecot 2.2.10 is now in the updates repo and can be installed via yum install dovecot. Horde can be obtained from remi's PHP repository, which features not only an up-to-date version of PHP  but also packages for Horde and various of its modules. After enabling remi's repo, a simple yum install php-horde-imp should be sufficient to give you a starter for a webmail installation based on Horde and IMP. You'll still have to configure it accordingly, though.As for MariaDB: The MariaDB folks haven't set up a repo for CentOS 7 and 10.x, yet. You can still use the CentOS 6 repositories for 7, but I'd advise caution as the packages for 6 don't fit that well into 7. E.g. they do not come with unit files for systemd, which is forcing systemd to use the shipped init scripts. Even worse, MariaDB-server 10.x is clashing heavily with mariadb-libs, which in turn is being pulled in as a dependency by a lot of packages such as exim-mysql. CentOS base repo is currently shipping MariaDB 5.5.37, which is the most current of the 5.5 branch. If you're content with that, use 5.5 for now and upgrade to 10.x once a repository for CentOS 7 is available. The alternative would be to compile a dummy rpm deprecating the mariadb-libs package, which essentially amounts to a dirty hack I cannot really recommend.If you decide to use 5.5 now and upgrade to 10.x later, be warned that this is everything but hassle-free in my experience. Safest way I found has been to create a complete database dump, clear /var/lib/mysql, upgrade to 10, feed the dump to the new version and run mysql_upgrade.Update: Upon closer inspection, it appears I've been talking rubbish. The MariaDB-shared package is statisfying the dependencies on mariadb-libs just fine. Install it and you'll be good to go.