The best way to access webmail is to go to the webmail URL. It is just the domain name with "/webmail" appended to the end.
http://yourdomain.com/webmail
Other ways include:
- Logging in via the cPanel and clicking the Webmail link
- Logging in from the Customer Centre. See this article to learn how: https://gesatech.net/knowledgebase/134/Webmail-Login-from-the-Customer-Centre.html