outlook doubles emails in inbox

[jdelcid]

I have a user who downloads his email from his home ISP, work ISP and
occasionally a tethered blackberry . Occasionally his emails will double up
when he downloads from work and then home at the end of the day. He
currently has one outlook email (profile) set up for downloading and 1 for
sending only (different SMTP server required at home). Does anyone know why
I would get his incoming emails doubling up?

 

[DL]

Sometimes integrated AV scanning causes this.
Disabling the AV integration doesn't always work, it may be necessary to
uninstall any AV, reboot, then reinstall AV without the Outlook
intergration.
Also a polling interval of less than 10 mins can cause issues