My asynch mail notification seems to have stopped since upgrading servers to 6.5.2. Asynch mail notifications are new email notification that come from the server to a client running from a local replica of the mail file.
From the Release Notes…
New Mail Notification Will Trigger an Immediate Replication with Local Mail File Replica
If you are using a local mail file replica and are connected to a network, a new mail notification from a server can cause an immediate replication of the mail file. When you have an open connection to a server that contains a replica of your mail file, that server can send the Notes Client a new mail notification outside of the Notes Client’s “Check for New Mail” interval. These notifications are sometimes referred to as “asynchronous” notifications.
If the Notes Client receives an asynchronous notification, and the “Mail Addressing” field in the Mail settings of the Location record is set to “Local and Server”, then an immediate replication of the mail file will take place.