Plugins not possible for outlook crm

Hi all, 

i tried to create a plugin for crm2011 (ru13). But in Outlook it wont work.

Error message ist:
Error registering plugins and/or workflows. Asynchronous steps are only supported in ServerOnly mode

Is it really true, that no one can use plugins for crm2011 in Outlook ... so it is only for direct use in Internet Explorer?

We have ifd crm on premise .. and our customers are encouraged to use crm in outlook plugin.

many thx for any kind of help.

Greets Pit