PiMail: Affordable, Lightweight and EnergyEfficient Private Email Infrastructure
Sufian Hameed, Muhammad Arsal Asif, Farhan Kamal Khan
IT Security Labs
National University of Computer and Emerging Sciences (NUCES)
Pakistan
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Introduction
 Electronic mail is one of the biggest technologies being used
over the internet today.
 Third party mail service is easier to use
 (-) Sacrifice of Control and Flexibility.
 Privacy is major risk
 Unauthorized Access
 Inspection during storage or broader gov. surveillance programs of
emails is of a major concern to a majority of the users.
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Can Private Mail Servers Help ?
 Private mail server allows full control over both the server and
the emails.
 Furthermore it gives complete access to mail server’s logs, and
access to raw email files in a user’s mail directory.
 One of the greatest benefit is the possibility to troubleshoot
and fix things on your own, instead of requesting a third-party
mail service provider.
 However, Running a private email server for individuals or
small scale enterprises can cost from $7 to $15 monthly or
more, depending on the configurations
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PiMail
 Affordable and lightweight mailing server for Individuals
and SMEs running on Raspberry Pi.
 A low cost infrastructure that would cost a one time
investment of $35 to purchase Raspberry Pi 2.
 Low electricity consumption with an email server that can
run 24/7/365 for under $5 of electricity per year.
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PiMail
 Personalized email address like MrX@mydomain.com with an
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annual recurring cost of domain registration with a registrar
like namecheap.com.
The ability to connect from anywhere, and read & send email,
using a secure IMAP connection on your phone, tablet or
computer.
Complete control over your personal communication.
Emails are stored over PiMail server, and nobody scan them to
sell adverts.
Smart spam filtering with SpamAssassin.
Efficient virus scanning with ClamAV.
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The Raspberry Pi Computer
 Raspberry Pi is low-cost, low-power and highly portable single
board computer.
 Raspberry Pi is one of the smallest, credit-card sized, single board
computer available in the market.
 It has the highest performance to cost ratio.
 Raspberry Pi makes it possible to create an affordable, energyefficient and portable miniature private mail server according to the
need of individual users or small enterprise..
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Raspberry Pi 2 - Hardware
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Raspberry Pi 2 – System Software
 The recommended OS for Raspberry Pi 2 is Raspbian, which
is a port of the well-known Linux distribution, Debian.
 Raspbian is optimized for the ARMv6 and ARMv7 instruction
set with hardware floating point support.
 It is optimized with around 35,000 pre-built packages, for
easy installation on Raspberry Pi.
 With the introduction of ARMv7 core, Raspberry Pi 2 can
also run Ubuntu and Pi 2 compatible version of Windows 10
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PiMail System Design
 PiMail runs Raspbian OS (a distribution of Debian optimized for the
Raspberry Pi hardware)
 Server runs on top of Raspbian OS (from 16 GB micro SD card)
 It is a combination of Postfix, SpamAssassin, ClamAV and Dovecot
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PiMail Components
Postfix
 A fast, easy to administer and secure Mail Transfer Agent (MTA)
developed by Wietse Venema in 1997 as an alternative to SendMail.
SpamAssassin
 One of the most widely used content-based filter
 The defense mechanisms include header tests, body phase tests,
Bayesian filtering, automatic address whitelist/blacklist, automatic
sender reputation system, manual address whitelist/blacklist,
collaborative spam identification database, DNS blacklist and
character sets.
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PiMail Components (2)
ClamAV
 Open source antivirus toolkit designed for the scanning of emails at
the mail gateways.
 Analyse the mail from the inbound queue using shared libraries of
the anti-virus engine.
 Dovecot
 Dovecot is a secure IMAP server that provide IMAP functionality
to fetch the mail from the mail directory.
 It is also used to provide simple authentication and security layer
(SASL) to validate the identity of a user before he can send or
receive an email.
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PiMail Testbed
 Augmented Raspberry Pi 2 with Postfix MTA, SpamAssassin
content filter, ClamAV antivirus and Dovecot IMAP server, and
deployed it over the LAN.
 For all the experiments, we used a desktop machine connected via
LAN to send mails with different size and frequencies to PiMail
server.
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Evaluation Scenarios
 We conducted experiments in four different scenarios as follows:
 S1: In scenario 1 (S1), the SMTP server runs postfix without any spam
filter.
 S2: In scenario 2 (S2) ClamAV is used as an anti-virus with Postfix.
 S3: In scenario 3 (S3) SpamAssassin is used as a content-based filter
with Postfix.
 S4: In scenario 4 (S4) SpamAssassin is used as a content-based filter
and ClamAV is used as an anti-virus with Postfix.
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Evaluation Metrics
 We run different experiments using the above scenarios to study the
impact of:
 Processing Delays
 End-to-End Throughput
 Message Size
 CPU and Memory Utilizations.
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Processing Delay
Settings:
 Two modes
 Burst (50 messages to saturate the mail server)
 1 second delay b/w two messages (50 messages)
 8 KB message size, being the average size of email message [12].
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Throughput
Settings (same as before):
 Two modes
 Burst (50 messages to saturate the mail server)
 1 second delay b/w two messages (50 messages)
 8 KB message size, being the average size of email message [12].
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Message Size
Objectives:
 Measure how message size effects the processing time and end-toend throughput.
Settings:
 Two message size i.e. 8KB and 64 KB
 Two modes
 Burst (50 messages to saturate the mail server)
 1 second delay b/w two messages (50 messages)
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Message Size Effect on Processing Time
Burst Mode
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1 sec Delay
Message Size Effect on Throughput
Burst Mode
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1 sec Delay
CPU and Memory Utilization
Objectives:
 Evaluate CPU and Memory Utilization of PiMail in all four
scenarios.
Settings:
 Sent email message of 8 KB every 0.6 seconds.
 Total evaluation time 480 seconds.
 This experiment setting is based on email statistics from a big
University discussed in [12]
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CPU Utilization
Total CPU (%)
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Avg. CPU (%)
Memory Utilization
Total Memory (%)
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Avg. Memory (%)
Processing Delay with Low Email Volume
Objectives:
 Effect of low volume email (without burst) .
Settings:
 50 emails of 8 KB each
 Interval of 60 seconds between two messages
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Conclusion
 We propose PiMail, an affordable, lightweight and energy-efficient private email
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infrastructure based on Raspberry Pi 2.
First extensive study that benchmarks the performance of Raspberry Pi used as a
portable and private mail server.
Based on the results, we observed:
 Content-based spam filtering with SpamAssassin is the most resource hungry
process.
 With high volume of emails, PiMail experienced performance bottleneck with
SpamAssassin
With an interval of 20-30 second, even the most decorated configuration of
PiMail (S4) will not exhaust the resources and there will not be any backlogs.
PiMail is capable handling a volume of 4000 emails with frequency 3 emails per
minute, which is more than enough for individuals and SMEs.
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Bibliography
[1] Clamav: Opensource antivirus engine for mail gateway. http://www.clamav.net/.
[2] Cost of private mail server. http://jeffreifman.com/how-to-install-yourown-private-e-mail-server-inthe-amazon-cloud-aws/.
[3] Dovecot: secure imap server. http://www.dovecot.org/.
[4] Postfix mail transfer agent. http://www.postfix.org/.
[5] Prism surveillance program. https://en.wikipedia.org/wiki/PRISMsurveillance-program/.
[6] Raspberry pi. https://www.raspberrypi.org/.
[7] Raspberry pi 2 model b. https://www.raspberrypi.org/products/raspberrypi-2-model-b/.
[8] Raspbian os. http://www.raspbian.org/.
[9] Spamassassin. http://spamassassin.apache.org/.
[10] Windows 10 for raspberry pi. http://www.WindowsOnDevices.com.
[11] T.R.P Foundation. About us. https://www.raspberrypi.org/about/.
[12] Sufian Hameed, Xiaoming Fu, Nishanth Sastry, and Pan Hui. Fighting spam using social
gatekeepers. Networking Science, 2(1-2):28–41, 2013.
[13] J. Klensin. Simple mail transfer protocol. the internet society, rfc 5321. The Internet Society, RFC
5321, 2008.
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