Yes you can, provided that you have Internet access and know your email account & password.
1. Open a Web browser (Chrome , IE , Firefox)
2. goto the url - www.example.co.za:2095 ('example.co.za' is replaced by your domain)
3. Type in your email address and password into the login page.
4. Now you will see a list of 3 various email clients that you may use (Horde, SquirrelMail, and Roundcube)
5. Choose and click to login using one of them.
In addition to the fantastic instructions above; In case you are connected to a network that utilizes a firewall which blocks access to certain ports, :2095 for example, you may use the following URL: http://webmail.example.co.za ('example.co.za' is replaced by your domain). This operates on the usual port 80