The Mail Source Agent (MSA) reports an error similar to:
"CMessage::CopyFromPST Error -2147024882 Not enough storage is available to complete this operation. File: 'MemStream.hpp' Line: '181' (Subject: '144FD98ABA9FAD439DD14916BCF073670000064C71F9', SourceKey: '144FD98ABA9FAD439DD14916BCF073670000064C71F9')"
for one particular mailbox and one particular message in that mailbox.
This is a known issue which does not have any workaround except for manual export to PST and copying a certain message to the target mailbox.
Neither increasing the PST size limit nor increasing the resource allowed for the agent to use will help, since the problem is related to the size of the memory allocated for the agent which is hard coded.
The limit for a message copied by the agent is about 200 mb.
To fix this issue:
Search the EMWMSA.log file for this certain error, retrieving the problem messages subject from the log file and exporting those messages to PST file; or
Login the mailbox having the problem, find the message and delete the message or attachment.