There were reports last night and this morning that user were having problems connecting to webmail. The problem appears to be linked to the Sophos PureMessage software and the timing of the quarantine digest messages and the slow disk array.
We updated our PureMessage configuration to send on digest messages instead of having each server send individual messages. The result being that all the messages hit the mail server and the same time and overwhelmed it with e-mail and client access with the start of the business day.
We are modifying the interval for digest messages from twice a day to once per day and moving the time to 1:30 am each morining.