SMSDOM will change a document from a Domino perspective so that we scan the message and when we are done we change the message back so that the router can then do it's job. This effects the modification date of the document but not the date of the message itself. This part of the process is not the culprit for degraded performance. Usually the problem is related to SSO being enabled which is not recommended for a cluster environment. SSO adds an encrypted tag to a message in order to reduce scanning processes if certain criteria are met therefore increasing performance. But in a clustered environment the writing and updating of this tag will degrade the performance of a clustered environment.