If you have configured integration between Lync Server 2013 Archiving and Exchange 2013 (for instructions please see here) you might see error event 56904 and warning event 56902 from LS Data Collection in the Lync Server event log.
These events are reported because the content to be archived is larger than what Exchange 2013 is configured to accept. Lync Server 2013 use Exchange Web Services to writes the content to Exchange.
To configure Exchange 2013 to accept the large content you need to set the MaxSendSize parameter of Set-TransportConfig in Exchange Management Shell to a suitable value. In my lab I use 40 Mb as the limit. The corresponding command is:
Set-TransportConfig -MaxSendSize 40Mb