Why i will have to soon stop using Zimbra email client

Hi ive decided to take some time of my busy time to register and let you know why Zimbra wont work for me anymore soon.

The reason is that i have too many emails. Im a web entrepreneur and each of my sites needs to have an email address, i have more than 30 different websites and i plan to keep growing this. Sadly in my Zimbra email client there is barely any room left for more email addresses on the left, now when i click one the zone to see the folders in it is getting super small. Cant this get a scrollbar to accomodate an infinite amount of emails?