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Jul 10, 2002
How To

Tips on Avoiding Spam Filters: How to Make Sure Friend-Get-a-Friend Viral Emails Get Delivered

SUMMARY: If your Web site or email campaign depends on a friend-get-a-friend feature, watch out. The email generated by your form may not get delivered properly. Here are some tips to fix the problem.
Recently a well-known email marketing executive called us up to
share her excitement about her new viral campaign. We were psyched
too; viral friend-tell-a-friend campaigns can be such a powerful
tactic to grow your opt-in email list.

Then our Tech Editor, Alexis Gutzman, started eyeing the way
the marketer's viral email was being sent. Turns out, the way the
email was sent meant that many big ISPs would filter it out as
"suspected spam" before it got to the recipient.

The whole problem had to do with the way the message "header" was
set up. It is something every email marketer should be aware
of, especially if you have a tell-a-friend function on your site
or if you use a third party email broadcast firm.

Here is a column on the header problem by Alexis. Read it over
yourself, and then pass it on to the tech team who send your
broadcast email.

-> Yes, Spam Filtering Affects Opt-In Emailers Too

Spam has increased by more than 600% in the past year. To cope
with the influx, ISPs such as AOL, Mindspring and Verizon, as well
as most big company IT/MIS departments are using spam filters.

This affects legitimate broadcast emailers, such as opt-in email
marketers and email newsletter publishers, because there is no set
way these various spam filters can know if the email is requested
opt-in or not. Currently the filters can only guess at what is
spam. Which means legitimate email gets caught up in the net along
with its less legitimate cousins sometimes.

To avoid being filtered, first you have to know that there are
three ways that ISPs filter spam:

1. By looking at the header of the message

2. By looking at the contents of the subject line or message body
to identify likely spam words and phrases

3. By subscribing to a blacklist service that provides an up-to-
date list of domains that have been identified as being used by

Today we are going to explain how to avoid being filtered based on
your headers. (We will cover avoiding the other two ways in future

-> Are Your Messages Already Being Filtered Out?

Are you already being filtered based on your headers?
Unfortunately there is no way to tell exactly how much of your
broadcast email is being filtered prior to reaching it's intended

Some ISPs that filter at the server level will send your message
back to you as a "bounceback." But not all. In fact AOL, among
others, does not send back filtered messages. (Another reason why
if you have a large slice of AOL email addresses on your list, make
sure you add a "seed" name of your own there to see if mail gets
through properly.)

Sometimes a lower-than-expected open or click rate will tip you off
that you have a filtering problem. Make sure that you
routinely check these metrics on a regular basis.

Luckily, even if you are not sure how much of your email broadcast
is being filtered, header filtering is one of the easiest things to

-> Headers Are Your Calling Card

Back when society was more civilized, you would visit an
acquaintance and hand your calling card to the butler. While you
waited patiently, your calling card would be delivered to the
acquaintance, who would decide whether he or she wanted to receive

In the email universe, your calling card is your header, and the
butler is the recipient’s mail server.

When you send a message to someone on your list, a conversation
takes place between your email server and your recipient’s. Your
email server sends the recipient’s email server just your header
(the FROM email address in your email message). If the recipient’s
email server does not like the way your header looks, it will reject
your message.

One way filters evaluate your header is by making sure it's the
same as the actual domain that is sending the email.

For example, if the FROM email address claims to be
“,” but the email server from which the message is
sent is “,” then the email server can reasonably
assume that the header has been falsified.

This sounds trivial, but falsifying headers can get you into big
legal trouble, as some ISPs including AOL have strict terms and
conditions for anyone sending them email and explicitly say that
they will delete mail with falsified headers and will prosecute
(and have successfully prosecuted) offenders.

When you send bulk email, it is easy to change the FROM address, but
it is much more complicated to disguise the identity of the sending
mail server. Spam filters understand this. They believe the domain
information. They do not believe the FROM address, nor should they.

-> Alert: You May Be Falsifying By Mistake

There are two scenarios under which you might be inadvertently
falsifying your header, without even realizing it is happening.

Scenario #1: You send email using a third party broadcast email
service (aka a "list host"), and you put your own FROM email
address, rather than a FROM address on the third party's server.

If you send email from a list host, make sure that the FROM email address is one that is hosted on their mail server. Ask them to
assign you one.

Yes, you can still put your FROM name as your own name. You
still should put your own email address as the REPLY-TO address.
Most human replies will go to the REPLY-TO address, rather than the
FROM address. Bounce messages often go to the FROM address (or the
BOUNCE address, if you set one up for that purpose).

Scenario #2: You have a “forward to a friend” feature on your site
or email messages, and when it sends email, it uses the referring
friend's email address as the FROM email address rather than yours.

We certainly see the logic of having the forwarded message come
FROM the trusted party. It is more likely to be opened, for one
thing, but this can get you into big trouble.

Quick fix: Rather than sending the message FROM the friend's email
address, send it FROM an address on your email server.

Be sure to use the friend's name at the start of the subject
line of the message, and the friend's email in the REPLY-TO
address. These two things will increase your open rates and pass-
along success.

However, we do want you to be aware that by forcing the first
friend to enter an email address, a first name, and a friend’s
email address, in order to use your forward function, you might
have raised the barriers too high for him or her to use the

Our best-practices workaround is a bit on the technical side, so
it is in the Tech Notes.

-> Boring But Necessary Technical Notes:

If you want to use an address on your own server for the FROM
address, set up an MX record on your Web server with a third-level
domain that points to the mail server of your list host.

For example, we have the address that
actually resolves (in the DNS) to our list host. Since the
recipient’s mail server will frequently check the DNS to make sure
your domain exists. Since resolves to the
IP address it is coming from, the messages go through no problem.

By having this MX record set up, you can have all subscribe and
unsubscribe messages also appearing to go through your own domain,
rather than

As part of testing your email campaign, you should have test
accounts set up with ISPs that filter on each of these bases
mentioned above, so that you can test what is getting blocked on a
regular basis. (We will cover testing in much more detail in a future

If you see any messages in your delivery report from recipients’
mail servers that “malformed headers” or something like that, it
may be that you are being filtered on this basis.

-> Best-practices recommendation for forwarding to a friend:

If you have a “forward to a friend” feature in your email message,
include a hidden field in the forward form to hold the recipient’s
email address.

You obviously have the recipient’s email address, since you are
sending the message to that address. When your reader clicks “send”
on the forward form, your server will know who is doing the sending
and will be able to apply the right REPLY-TO address without having
to ask for it.

This feature won’t work on your Web site unless you have cookies in
place with visitors’ email addresses, which is something you might
want to think about adding. It is relatively trivial to update your
cookies with email information from an HTML newsletter or from the
opt-in thank-you page on your Web site.

Good Luck!
See Also:

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