You have the option of using two different webmail applications of us nowadays.
Roundcube (which we recommend) and Squirremail which is the version we had since a long time back.
There are some compatibility issues between them. Eg not shared address books, filters created in one webmail can not be modified in the other.
Do you have other wishes on webmail client? Send an email to support(at)spacedump(dot)se and we will examine the possibilities to install it.