The "Automatically switch mailboxes with unsynchronized mail size" option in the mailbox collection properties may cause unexpected agent behavior. Selecting this option may lead to the expectation that the Mail Source Agent (MSA) leaves unsynchronized data in the mailbox. To clarify, this option controls how much data the MSA can synchronize within a single session to switch a mailbox. Similarly "If not more than ... errors occurred during migration" option refers to the amount of errors occurred during the current synchronization session when mail switch is attempted.
The described mailbox switching logic is true as of QMM 8.6 and EMW 4.0.1 for all previous product versions.
The Mail Source Agent(MSA) only keeps information about data that has been processed (or errors that occurred) in the last session. During each session the agent tracks the amount of data exported to PST file (or errors occurred) for each mailbox with the following considerations for the "Automatically switch mailboxes with unsynchronized mail size" and "If not more than ... errors occurred during migration" options:
- If the data size (amount of errors) exceeds value specified in the "Automatically switch mailboxes with unsynchronized mail size" ("If not more than ... errors occurred during migration") option, the MSA will not switch the mailbox during the current session.
- If the data size (amount of errors) is under the limit, the MSA will switch the mailbox.
This behavior allows you to optimize switching of heavily used mailboxes and ensure the Target Mailbox contents are fully synchronized with the source.
For example, you have 1 KB set in "Switch with unsynchronized email size". What this means is that a mailbox switch only happens if last session gathered less than 1kb worth of email from the source mailbox. Since mail keeps arriving to the source mailbox, the Mail Source Agent always has something new to send to the target and as long as that packet is over 1Kb, the mailbox will not be switched. It is safe to set this to 1000Kb, then if last MSA packets is <1Mb, mailbox is switched. It doesn't mean that this email will remain unsynchronized, MSA will still do two more cycles on source mailbox after successful switch and bring over any unsynchronized email.
The unsynchronized email size is a very dynamic value, and it keeps changing as mailbox grows. Even right after all mail has been taken across while the switch is going on, or replication in AD goes through, new mail can arrive to the source mailbox, so in any case chances are there will be unsynchronized email, that's what the next two cycles are for. To rephrase: we have the UI setting at XXX KB. TheMSA goes through source mailbox and gathers any new email since last cycle. The PST file is generated (or is empty if there is nothing new). The Size of PST is compared to UI setting. If PST size is *less* than the UI limit, mailbox is switched. To be perfectly precise the closest name for this option in UI would have to be "Switch mailbox automatically when there was less than XXX KB of new (unsynchronized) mailbox content gathered in last session.
