but reading the link it points to (http://php.net/manual/en/intro.mcrypt.php) in the installer page I can read that
QuoteThis extension rely in libmcrypt which is dead, unmaintained since 2007.
Please don't rely on it, consider switching to well maintained alternatives (openssl, crypt, password hashing functions, phpseclib, password_compat...)
So, should I or shouldn't I install it ?
The installer check for mcrypt was remove for Roundcube 1.2, I'm not sure when the actual mcrypt functions where removed from Roundcube but I say your safe to not use it.
Thanks SKaero.