AV was not preinstalled. I installed it.
I've removed and reinstalled the product now multiple times.
If AV is not installed, OUTLOOK works fine.
If AV is installed and Mail Shield is enabled, I get encryption errors when trying to send/receive email.
If AV is installed and Mail Shield is disabled, Outlook works fine.
If AV is installed, Mail Shield is enabled, and I untick scanning inbound and outbound emails, I get encryption errors when trying to send/receive email.
I haven't tried having Mail Shield enabled and going through unticking all the other Mail Shield options one-by-one yet.