As mentioned above, ISP Spam Filters utilize a variety of tools and processes to identify incoming emails as possible spam.
They look for spam-esque characteristics, calculate the likelihood of the email being malicious or spam, and then weigh the total risk against a predetermined threshold. If it is too high, the email is flagged as spam.
Typically, the tools analyze:Email headers –
focusing on suspicious email addresses or ones that have not gone through a checklist for deliverability
, or aspects such as misspellings.Email content –
Filters will check for file names, bolded or italicized or all caps, text size, images, and attachments.Blacklist filters –
they will compare IP addresses and domain names to those of senders on existing blacklists, as they can cross-examine. Utilizing tools to warm up
and determine if you’re on a blacklist is very important when setting up a new domain.Permissions
– filters will compare to what the recipient has previously agreed to receive from the sender. Anything that has not been agreed upon will go to spam.Rule-based filtering
– these are the filters set up by algorithms to identify spam, such as particular phrases. There are particular words or phrases that spam checkers will help you recognize and avoid.