All sidebar moderators share a mailbox for that userid.
As to reporting, the abuse button is best. It gets our attention a little quicker and there is a log of every abuse report. If you send us an email about a problem post, we won't know, while reading the email, if others have reported it or if other moderators have already acted on it.
When we're reading abuse reports, all of the latest abuse reports are right there in front of us for reference as well as what actions another moderator may already have taken.
Save the freepmail for communication and use the abuse button for just about everything else.