One of the nicest examples of email steganography that I've seen is Spam Mimic. It hides a message in a spam-like format.

For example here is an encoding of a short well known phrase: ;-)

Dear Friend , Especially for you - this amazing announcement 
! We will comply with all removal requests ! This mail 
is being sent in compliance with Senate bill 2216 ; 
Title 3 ; Section 301 ! This is different than anything 
else you've seen . Why work for somebody else when 
you can become rich within 62 weeks . Have you ever 
noticed more people than ever are surfing the web and 
most everyone has a cellphone . Well, now is your chance 
to capitalize on this ! We will help you decrease perceived 
waiting time by 200% and process your orders within 
seconds . The best thing about our system is that it 
is absolutely risk free for you . But don't believe 
us . Mrs Simpson of Arizona tried us and says "My only 
problem now is where to park all my cars" . We assure 
you that we operate within all applicable laws . DO 
NOT DELAY - order today ! Sign up a friend and you'll 
get a discount of 20% . Thank-you for your serious 
consideration of our offer . Dear Cybercitizen , This 
letter was specially selected to be sent to you . If 
you are not interested in our publications and wish 
to be removed from our lists, simply do NOT respond 
and ignore this mail . This mail is being sent in compliance 
with Senate bill 2616 , Title 3 , Section 307 ! This 
is NOT unsolicited bulk mail ! Why work for somebody 
else when you can become rich inside 15 MONTHS ! Have 
you ever noticed nobody is getting any younger & people 
are much more likely to BUY with a credit card than 
cash . Well, now is your chance to capitalize on this 
. WE will help YOU SELL MORE & SELL MORE . You can 
begin at absolutely no cost to you ! But don't believe 
us . Ms Jones of Ohio tried us and says "I was skeptical 
but it worked for me" ! We are licensed to operate 
in all states ! We BESEECH you - act now ! Sign up 
a friend and you get half off ! God Bless .
[download]

John.
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