Sorry, you're correct. those are in Tracing folder. the items that you see might be something to do with the EWS. can you check that client have any EWS related issues?

One of our user has very large cache files under \Users\username\AppData\Local\Microsoft\Communicator\username@domain.com

the cache file name are like this:  MailItemusername@sipdomain_someRandomDigits.cache

the size of these files can increase to Giga byte.

However, other files under the cache folder have normal size. such as ABS cache, endpointconfiguration cache,GalContacts etc..

What is the MailItem.cache files?

Hi,

check the Lync client if the logging is enabled. id so turn of the logging and restart the PC. 

Hi Thamara,

The lync client logging files is in the folder C:\Users\username\Tracing\

My issue is the cache files not the logging files.

Hi,

Actually you can remove the cache file in Lync profile folder. After removing it, lync would re-configure the user account information when connecting again.