Only disable Email scan on startup (with very large emailbox)?

Hi,

Can i disable only the email scan on startup for a user?

We have a user who only works 1 (or 2) day(s) a week and when he comes in for work and starts his email client (Thunderbird 3.1.x) his system slows down to a point where he can hardly do anything!
And because his email box receives hundreds of emails (because of monitoring/diagnose software such as Nagios for example sending emails almost every 15/30 min) this takes a very long time (about an hour or so!)
After the scan is complete the user briefly goes through some mails and deletes the rest.

Would it be possible to only scan for new incoming mails when the email client has already been started?

We are using ESET NOD32 Anti-Virus Client version 4.2.71.2
and Server version 4.0.138