Mac
7
Outlook is pulling from your email server some email that has an infected attachment.
Unfortunately clearing the local cache of outlook is not the permanent solution as you will simply re-download the email.
Couple of options here. First you can disable the avast real-time shields then let outlook download the messages, find the message with he bad attachment and permanently delete it (remove also from the deleted items folder). Second as Pondus describes, you can use a webmail type access to find and delete the message if you have that type of access.