"Why can't I send this message?"
A frequent question we get from our customers is “Why did my
mail bounce?”
They refer to a situation when they send an email message,
and after a few moments there’s an automated reply. Usually from “Mail Delivery Subsystem” or
a similar system information message.
Before I get into what those things mean, a quick look at
how email works.
Email: Greased Lightning
 |
| Basic Email Communications |
Mail doesn’t just go from your computer to the recipient in
one connection.
Mail goes from your computer to the mail server, through a
firewall, across the internet (where there can be 10 or more stops in alone),
then through the recipient’s firewall, their server, and finally their
workstation.
There can be even more stops with routers and other mail
filtering systems, but I’m just showing the basics here. Despite all these stops, everything typically
happens in a matter of seconds.
The Process
The sending workstation passes it to the sending mail
server, where it should be checked to see if you are a valid sender. It passes through the sender’s firewall and
on to the Internet.
The receiving firewall can (if it is configured to) check
mail for spam, validate a legitimate sender, checks the mail for viruses, and after
filtering, and passes it to the receiving mail server.
The receiving mail server can (if it is configured to) check
mail for spam, validate a legitimate sender, checks the mail for viruses, and after
filtering, and passes it to the recipient’s computer.
Here are some common scenarios when mail gets bounced:
Receiving Server Bounces
If the sender is determined by the receiving server to be “fake”
then mail can be denied. “Fake” would
mean that the sending server is pretending to be something it isn’t. Sometimes these messages bounce, but many
times they don’t, to prevent a spammer from knowing if they were successful or
not.
If the receiving mail server (after it’s gone across the
internet) finds that the recipient doesn’t exist (or is misspelled for
example), it will bounce the mail. You
may or may not get bounces for this, since many spammers will just guess at an
email address once they know the domain name.
Mail Bounced For Spam
There are a multitude of reasons for this. Here are a few:
- You use a 3rd party mail host (in
other words you don’t own your own mail server on-premises), and one of the
outbound mail connections was “blacklisted” because another client spammed from
the same host. Your outbound mail shares
the same connections and can occasionally be tagged as spam.
- The content of your email message is likely “scored”
as spam. Every email message has a “score”
for spam. No subject line increases the
score. Having an image or attachment
with no message included explaining it increases the score. Not identifying a sender increases the
score. Avoid this by always putting a
subject line, explain any attachments included, and don’t clear out your “from”
field.
- Your mail server is not “registered” on the
internet. Many mail servers will
validate the sending server by performing a “reverse lookup”. Much like our telephone system, you can use caller
ID to identify the caller. Mail servers
can cross reference the incoming communication against who it should be coming
from in the “from” field and weed out spammers.
Message Too Big
Most servers have limitations on what size of emails can be
sent or received. These bounces can come
from your own mail server if you have a limit on outbound mail size. Generally speaking, you want to keep your
email attachments under 10 MB in size (no more than 5 high quality photos, a
document under 300 pages, etc.).
Mail Delay
Sometimes the bounce message isn’t a bounce at all. At times, there is congestion on the
internet. If your sending mail server
cannot send a message after 2-3 tries*, it will wait 4 hours* to try
again. The delay message is sent to you
as a warning that your message is queued for delivery and may not try again for
several hours*.
Your mail server will continue to attempt to send the mail
for 2 days*, and if still fails, will then bounce the message back to you.
*These are configurable settings; typical defaults are
given.
Email isn't perfect…
Over 140 Billion emails are sent globally every day. Arguably, over 60% of that is spam. Despite that, the majority of our mail is sent
on time, and error free.
If your electronic message is important, it’s always a good
practice to just follow it up with a quick phone call.
To learn more about how email works for your organization or
get your bounced email messages analyzed to determine what’s going on, you can
contact Stewart and Son! Call us
today! 253-961-5068
You can read more from Wade at Stewart and Son by visiting the following blog sites:
Content Copyright Wade Stewart (C) 2013
Labels: configuration, customization, email, exchange, industry, IT, managed services, server, small business