# How to Protect Your Email from Spam

#### DKIM

DKIM (DomainKeys Identified Mail) is a cryptographic method for signing mail. Mail is signed with the private key on the mail server. The public key may be retreived from the domains TXT record for verification.

---

#### SPF

##### WORKING

The SMTP protocol was not originally designed to be very resistant to spoofing. SPF tries to help by reading rules about sender servers from the domain TXT records.

##### PROBLEMS

SPF does not take redirected mail into account. Due to SPF, all redirected mail would be discarted as fake.

##### RECOMMENDATION

Don’t use SPF. Instead, use DKIM.

Further reading:  
[Wikipedia](https://en.wikipedia.org/wiki/Sender_Policy_Framework)  
[Why you shouldn’t jump on the SPF bandwagon](http://david.woodhou.se/why-not-spf.html)  
[Sender Policy Framework project](http://www.openspf.org/)

---

#### DCC

DCC (Distributed Checksum Clearinghouses) creates a checksum from all mail. If the same checksum is detected many times, the spam score is increased.

---

#### PYZOR

Pyzor is an offspring of Razor and works in a similar manner. Mail checksums are collected and checked against multiple rules on central servers.

---

#### RAZOR

Razor is a closed source community spam filter. Further reading: [Vipul’s Razor](http://razor.sourceforge.net/)