The Simple Mail Transfer Protocol (SMTP) is the most
commonly used internet based protocol for third party
SMS delivery. Almost every major carrier in the US and
Canada supports this protocol and, as a result, this
is the most heavily used protocol. The down side to
this protocol is that it is effectively Email, which
means that there are a lot of issues that can arise
from using it. For a brief primer on the SMTP Protocol
in general, as well as the sub-components (such as PTR,
SPF, A, MX and MTA records), have a look at The Email
School: http://wireload.net/category/the-email-school/
There are two primary ways to send SMTP: Direct Delivery
and Relayed Delivery.
Different networks handle SMTP and its related ports
in different ways. If port 25 is free and clear (i.e.
not blocked by any firewalls along the way), you can
attempt to use the Direct Delivery method. However,
this method of delivery does rely on your Internet Service
Provider's settings, and general spam reputation on
the internet.
Sometimes, even if port 25 is open, you still can't
use the Direct Delivery method for SMTP because your
Internet Service Provider's (ISP) Message Transfer Agent
(MTA) is considered untrustworthy. While this is the
most common cause of direct delivery SMTP failure, it
is important to note that this is not the only cause.
In any event, when this happens, the ISP's public IP
range appears on several blacklists dedicated to providing
third party insight in to trustworthy and untrustworthy
sources of SMTP traffic. It is also worth noting your
ISP's IP range covers anyone on their internet service,
not just your network. Any IP address on one of these
blacklists is treated as an untrustworthy source and,
as a result, any direct connection attempt to a receiving
SMTP system, such as those for cell phone carriers that
subscribes to these blacklists, will fail.
The first step in resolving this issue is to find your
public IP address. The easiest way to do this is to
go to the following website, from the computer that
is sending out the SMTP messages:
http://whatismyipaddress.com
Next you will want to find out if your IP address is
listed with one of the major blacklists. There are a
variety of resources available for this, such as:
http://whatismyipaddress.com/blacklist-check
http://www.mxtoolbox.com/blacklists.aspx
http://www.senderbase.org/home
Once you have determined what your public IP address
is, go to one of these sites and perform a blacklist
check on it. In the results of the lookup, you should
see which, if any, blacklists your IP address is listed
on.
If you find that your IP address is listed, you have
a few options:
1) Attempt to delist your specific IP address from
the blacklists by notifying them of the problem.
2) Contact your Internet Service Provider and inform
them of the MTA downgrade and resultant blacklisting.
Hopefully, your ISP will work with you to resolve their
IP range's status as untrustworthy.
3) Change your method of delivery to relay through
an SMTP server.
Each blacklist has a website associated with them and
most have a procedure for delisting specific IP addresses,
because false positives can happen. Earlier, we mentioned
that your IP being listed as a result of your ISP's
IP range being untrustworthy, is only one possibility
for your IP being listed with the blacklists; When you
perform the blacklist lookup on your IP address, pay
attention to the results. Sometimes, if a system or
server on your network is infected with a particular
type or style of malware, your specific IP will be blacklisted.
The lookup pages will provide the information relevant
to why your IP was listed.
Once you've determined that your IP address is listed,
you can submit a delisting request with the blacklist
hosts. These requests generally take a minimum of one
business day to process and once the request has been
approved, your IP will be removed from the blacklist.
However, this may not be the end of the process. If
your IP was listed because you have a malware infected
system on your network and you don't identify and remove
the malware, your IP will immediately be listed again.
Similarly, if your ISP's IP range is listed, rather
than just your specific IP being listed, your IP will
immediately be listed again.
The complexity is that there is only so much that you,
the end user, can do to resolve the issue as a great
deal of this has nothing to do with your network and
everything to do with your ISP's standings with the
aforementioned blacklists. It is also important to note
that if you repeatedly submit delisting requests to
the blacklists without resolving the issues that caused
your IP address to be listed in the first place, you
will be permanently blacklisted and can never submit
another delisting request for that IP address without
going through a very long, intensive and cumbersome
process involving contacting the lists directly. It
is very important that you not overuse the delisting
request function.
There are some notable exceptions to this, however.
Certain Internet Service Providers, such as Comcast
and COX Cable, require that all SMTP traffic from their
networks MUST be passed through a Comcast or COX Cable
SMTP server for non-business internet connections on
their service. Even for some of their business internet
services, even if you have your own SMTP Mail server
with an associated A, MX, PTR and SPF record, you may
never be able to use direct delivery for SMTP due to
the restrictions placed on the ports and the general
status of the MTA, PTR and SPF records for your ISP
and what they have or have not redirected to your own
SMTP server, if you have one.
In any event, if your IP address has been listed because
your ISP's IP range has been flagged as a potential
source of spam, submitting a delisting request won't
do you any good and it leaves you with only two options:
1) Contact your Internet Service Provider and inform
them of the MTA downgrade and resultant blacklisting.
Hopefully, your ISP will work with you to resolve their
IP range's status as untrustworthy.
2) Change your method of delivery to relay through
an SMTP server.
It is possible that your ISP may not be aware of the
issues regarding their IP range. You can attempt to
show their Tech Support the results of your blacklist
lookups and they may or may not take any action to resolve
the issue. If they do take action to resolve the issue,
you should be able to resume using direct delivery for
your SMTP messages. This process, however, can sometimes
take months to resolve which leads us to the final option:
Change your method of delivery to relay through an SMTP
server.
If your IP address is listed on the blacklists and
you can't get it delisted and your ISP won't work with
you to resolve the larger issue with their IP range,
your only option is to relay your messages through an
SMTP server that you have access to. Most ISP's have
an SMTP server that they will grant you access to for
using their internet service and most companies have
their own SMTP Server available on their intranet. There
are three questions you'll need to have answered in
order to use this method of delivery:
1) What SMTP server do you have access to?
2) Does that server require authentication? If so,
does it support LOGIN, PLAIN or CRAM-MD5 as methods
of authentication?
3) What specific authentication credentials should
you use to authenticate your SMTP traffic?
Once you get those three questions answered, you can
then reconfigure SMTP for relayed delivery instead of
direct delivery.
If, however, you don't have an SMTP server available
to you, you can't have your IP address delisted from
the blacklists and your ISP isn't willing to work towards
resolving the larger issue with the MTA, there is a
last resort option. You can use a third party mail relay
service, such as DNS Exit, for SMTP delivery. The benefit
to this is that most third party mail relay services
will listen for SMTP traffic on non-standard SMTP ports,
which are typically monitored or blocked by local firewalls
and ISP's. The drawback to this is that third party
mail relay services do charge fees to use their services
and the fees are often based on the number of messages
you need to send.
About the Author -
Sharon Housley is the VP of Marketing for NotePage,
Inc. a software company for communication software solutions.
http://www.notepage.net
System Requirements |
|
Processor |
Pentium 500
mhz or better |
Memory |
128 Mb of RAM
(typically 256 Mb total memory for Win 2000, XP,
2003, or 1 Gig for Vista) |
Hard
Drive |
50 Mb Hard
Drive Free (for application & database)
|
Connectivity |
300 baud or faster modem
for dialup connections
serial cable for direct connections or a
dedicated Internet connection |
Operating
System |
Windows
2000, XP, 2003, Vista (32 bit) |
|