Blacklisting is best used to combat the messages that you know you will never want, although they might not be spam to everyone.

Go to Management
Go to Inbound Filtering
Go to Blacklist

IMPORTANT: Do not blacklist your own address or domain, as there are certain times when legitimate email from these addresses arrives externally.

Blacklist by “From” Address - Enter addresses, one per line, which you would like to automatically block without exception.
Acceptable formats include:

user@domain.com - (all mail from this address will be blocked)
domain.com - (all mail from all users from this domain will be blocked)
.com - (all mail from .com domains will be blocked)

Suggestions:
Try not to pre-populate the blacklist with a large number of domains, but rather use it as a tool to block recurring spam sources
Marketing emails you may have inadvertently opted into are a good blacklisting candidate, although you also have the option of clicking unsunscribe if the sender seems reputable (i.e.: retail store marketing newsletter)

Blacklisting for each piece of spam that reaches you is unnecessary and ineffective, as most spammers don’t use the same address repeatedly.

Blacklist by Subject - This tool will allow you to have selected messages automatically classified as spam by the subject line.

Add entries based upon:
Exact match
Begins with
Ends With
Contains (recommended)

These Blacklisted by Subject entries will be visible in your digests and quarantine (but not your inbox) unless you have Hide Egregious Spam enabled, as we have to accept the message to analyze the subject

Same format rules apply if blacklisting at USER level.