If you receive SPAM emails that look they are coming from your own email account, or from other people with email accounts on your same domain, they are not really coming from those people's accounts. As a standard practice, spammers spoof the "From" email address (this is very easy to do) and populate it with other email addresses that they have stolen. So other people are getting SPAM that looks like it is from you. Now what they love to do, is match up emails from the same domain names, so it looks like one person from your team is sending an email to another.
These emails usually get marked as SPAM by our filters on the server, but they can often elude the junk mail rules on your local computer's mail program (e.g. Outlook, Apple Mail, etc.) because these rules often include exceptions for senders that are in your address book.
There are only two options that we can suggest, and neither are very helpful. Either turn off the rule exception which excludes people in your address book from being marked as SPAM, and regularly check the spam folder to make sure no legit emails were marked as SPAM (it would be rare). Or just delete the SPAM from your team mates, when it comes into your inbox.