Content Filter Settings Domain-wide
The Administrator can select default settings for the entire domain. If the settings for a particular mailbox are not deliberately selected and modified, it will use these settings.
Spam Filter Settings
The Anti-Spam filter settings have the most options. You can choose from various presets for filtering, or customize your own, with any level of granularity.
Messages that are spammy can be delivered with their subject lines rewritten. Spam messages can be quarantined. And you can choose the score at which each of those happens. Our standard setting quarantines mail at a score of 7.0. But you might want to make this number higher or smaller, or add the option to rewrite the subject. It's entirely in your control.
Anti-Virus Filter Settings
Your options for virus-infected emails are much simpler: Do you want to be notified when a virus-infected message is quarantined?
Message-Size Filter Settings
You can opt to reduce the maximum allowed message size for your email. Our maximum is 150MB.
Banned File Types Filter Settings
Banned File Types are messages that contain various types of dangerous enclosures. The standard filetypes blocked by this filter include: '.bat', '.cmd', '.com', '.cpl', '.dll', '.exe', '.pif', '.scr', and '.vbs'.
These restrictions apply to files embedded inside other files, like zip or tar files too.
Besides quarantining these emails and deciding if you want a notification, you can allow them to be delivered. You can even set a "plus extension" for delivery, so you can have the message delivered to a variant of your email address, like firstname.lastname@example.org Some people like to use this to support client-side filtering.
Bad Headers Filter Settings
The Bad Headers filter has the same options as those for the Banned File type filter. Bad headers are messages that violate the internet-standard RFCs. The checks include verifying the MIME structure of an email message, checking for control characters (like NUL and CR), looking for improperly encoded 8-bit characters in an email header (per RFC 5322), and headers longer than the maximum allowed length of 998 characters (per RFC 2822).
Of all the things here, this is the one most likely to have a false positive, particularly with various mailing lists. You might opt for delivery of these messages. Or deliver it with an extension. Or, if you do want to quarantine it, enable the notification option shown below.