A spam is an unsolicited mail.
It's also known as:
- Unsolicited Bulk Email (UBE)
- or Unsolicited Commercial Email (UCE)
Ham vs Spam
The opposite of Spam is known as Ham for a legit email
The ratio of ham/spam is:
- for blog (90%) (comment/trackback)
- for email (98%)
With mail authentication:
- your mail server needs to be listed publicly
- your mail needs to be signed
For more information, see What is Email Authentication?
Greylisting 2) is based on the fact that a Spam server will never try to send the email again, the first email received from an unknown sender is rejected and is placed in a greylisting, and if the SMTP server sends it again after the grace period, the sender is placed on the whitelist.
spamd has a rejection based on greylisting.
Blacklisting / IP Blocklist
A list of IP/mail that should be blocked. Email - Blacklist
Spam may be indirect.
- when a comment is posted, an email is send to the subscriber and the administrator receive it.
- or via blog trackback
A spam trap is an email address that’s not actively used but is actively monitored. If a spam trap receives an email, something is rotten because that email address never opted in to receive emails.
Spam emails use the unsubscribe option to confirm that your email is in fact legit and active.