A lightning talk given to WordPress Portsmouth about the use and implementation of the Sender Policy Framework

1. Sender Policy Framework
Help Protect Your Inbox From Basic SPAM
Wordup Pompey 20th February 2019
Scott McKeown

2. What is SPF?
• An eMail authentication method
• An open standard
• Simple to enable

3. Short History Of SPF
• 2000 First mention of an SPF idea
• 2002 SPF-like specification published
• 2003 RMX & DMP specifications merged
• 2004 Renamed to ‘Sender Policy Framework’ from ‘Sender Permitted
From’ and MARID task group formed
• 2005 MARID group collapsed and revert to ‘classic’ SPF idea
• 2006 Experimental RFC published for SPF
• 2014 RFC-7208 published

4. How does SPF Work?
Write an eMail eMail Server SPF Record Check
SPF Fail
eMail Server SPF Pass

5. Where does it go?
DNS Zone file as a Text (TXT) Entry.

6. SPF Record Make Up
• Three Sections
• Domain or Subdomain
• SPF Version
• The Mechanisms (Rules)

7. The Domain or Subdomain
SPF Sections

8. SPF Version
SPF Sections

9. The Mechanisms (Rules)
• Prefix
• + Pass
• - Fail
• ~ Softfail
• ? Neutral
• Can be applied to ANY of the SPF Mechanisms (Rules)

10. The Mechanisms (Rules)
• all
• ip4
• ip6
• a
• mx
• ptr
• exists
• include

11. Examples
Allow domain's MXes to send mail for the domain, prohibit all others
v=spf1 mx –all
Allow any IPv6 address between 1080::8:800:0000:0000 and
1080::8:800:FFFF:FFFF
v=spf1 ip6:1080::8:800:200C:417A/96 –all
The current-domain is used
v=spf1 a –all
Use External Mail Server
v=spf1 mx mx:deferrals.domain.com –all
Include Other Domains SPF Rules
v=spf1 include:example.com -all

12. Lets Write Our Domain Rules

14. Example Of Blocked eMail
Feb 20 11:58:04 ms1 postfix/policy-spf[3987]: Policy action=550 Please see
http://www.openspf.net/Why?s=helo;id=redithosting.co.uk;ip=5.2.18.104;r=ms1
.redit.co.uk
Feb 20 11:58:04 ms1 postfix/smtpd[2236]: NOQUEUE: reject: RCPT from
unknown[5.2.18.104]: 550 5.7.1 <yoqiihld@redithosting.co.uk>: Recipient
address rejected: Please see
http://www.openspf.net/Why?s=helo;id=redithosting.co.uk;ip=5.2.18.104;r=ms1
.redit.co.uk; from=<> to=<yoqiihld@redithosting.co.uk> proto=ESMTP
helo=<redithosting.co.uk>
Feb 20 12:26:08 ms1 postfix/policy-spf[6230]: Policy action=550 Please see
http://www.openspf.net/Why?s=mfrom;id=users@email.address;ip=95.105.89.221;
r=ms1.redit.co.uk
Feb 20 12:26:08 ms1 postfix/smtpd[2236]: NOQUEUE: reject: RCPT from
unknown[95.105.89.221]: 550 5.7.1 <support@redit.co.uk>: Recipient address
rejected: Please see http://www.openspf.net/Why?s=mfrom;id=
users@email.address;ip=127.0.0.1;r=ms1.redit.co.uk;
from=<AndrewMorgan@ufanet.ru> to=<support@redit.co.uk> proto=ESMTP
helo=<127.0.0.1.public.ip.address>

15. References
• https://en.wikipedia.org/wiki/Sender_Policy_Framework
• http://www.openspf.org/
• https://www.gov.uk/government/publications/email-security-
standards/sender-policy-framework-spf
• https://tools.ietf.org/html/rfc7208