Ahm just to clarify - Desktop isnt nessesary wrong Term.
Only thing is you (and looks like not even your Provider) isnt relaly familiar with Groupware Products
No matter if oyu use Lotus Notes/Exchange-Outlook or Zimbra
At the Moment you use a Groupware System your Account will never be like an POP Account
Its always a Mirror - This is the case even in outlook when connecting to exchange - and that the way todo it
Also that your Provider mean that POP3 is the solution sounds a bid Odd - isnt that a backstep (huge one)?
I think their hotline just wanna get rid of that suport case asap hehe...
No there 2 Possibilities why this happen
1 - one of your Mailprogramms uses pop3 and delete those Messages
2 - your isp delete automatically mails after xxx Days - actually zimbra got this feature - usually only used for trash and spam box to purge but it can be set for inbox too
So what you should tryout is -
First change your password - so you make shure you didnt forgot about any mailclient could access your account - or even another person
Second set ZDesktop account to Zimbra and Sync your box
If mail still dissapear its very likly your ISP do this
- its also likly that if they got a regular Hotline they dont know about it - you may need a higher Support Level to get answers then
Its worth a try - and forget outloook
