Understanding
Mail Delivery Errors
If you send an
e-mail that for some
reason can't be
delivered, either
our mail server or
the mail server
where the error
occurred sends a
mail delivery error
report back to you.
Some of these error
reports are pretty
cryptic, so we
receive a fair
number of "Why did
my mail bounce
back?" questions.
Let's look at
some of the most
common mail delivery
error reports and
try to decipher what
they mean. If you
receive a mail
delivery error
report not shown
below, can't figure
it out, and want to
know what it means,
forward it to
ispadmin@comsouth.net
for interpretation.
WARNING:
Don't be fooled by
phony mail delivery
error reports! If
you receive one that
claims to be from
"postmaster@comsouth.net"
or "postmaster@mail.comsouth.net",
it is a fake that
may carry a virus.
Mail delivery error
reports originating
from comsouth.net's
mail system always
show "Mail Delivery
Subsystem
<MAILER-DAEMON@mail.comsouth.net>"
on the "From: "
line, never
"postmaster".
Almost all mail
delivery error
reports begin with
something like the
following:
----- The following addresses had permanent fatal errors -----
<JDOE@HOME.COM>
That tells you
that your mail to
the specified
address could not be
delivered. It may
also tell you
whether the error is
a "permanent fatal
error" (one which
makes it impossible
to deliver the
message) or a
"transient non-fatal
error" (just a
temporary setback,
and the mail server
will keep trying).
A more complete
description of the
problem is usually
next, in a section
labeled "Transcript
of session follows".
Below are the more
common ones, each
followed by an
explanation. These
are taken from
actual delivery
error reports, but
the usernames have
all been changed to
"jdoe" to protect
the privacy of the
actual addressee.
The examples
below are all mail
delivery error
reports generated by
Sendmail, the
predominant mail
server software on
the Internet. Error
reports generated by
other mail server
software (QMail,
Postfix, Microsoft
Exchange, or
whatever) may look
different, but will
contain the same
basic information.
User Unknown
----- The following addresses had permanent fatal errors -----
<JDOE@HOME.COM>
(reason: 550 5.1.1 <SBEMIS1@HOME.COM>... User unknown)
----- Transcript of session follows -----
... while talking to mx-rr.home.com.:
>>> RCPT To:<JDOE@HOME.COM>
<<< 550 5.1.1 <JDOE@HOME.COM>... User unknown
550 5.1.1 <JDOE@HOME.COM>... User unknown
Instead of "user
unknown", you might
see "unknown user",
"invalid recipient",
"not a valid user",
"mailbox
unavailable", "not
known here" or
something else
expressing the same
idea.
In this example
our mail server
tried to deliver the
message to the mail
server at home.com,
but the home.com
mail server refused
to accept it because
they have no user
known as "jdoe".
This could be
because the username
part of the address
(jdoe) was typed
incorrectly, or
because the "jdoe"
account at home.com
expired or was
cancelled, or
because you were
trying to reply to a
message sent out
under a falsified
address. In rare
cases it can
indicate a mail
system failure at
the remote site.
- What you
should do:
- Confirm the
intended
recipient's
address, if
possible. Resend
your message to
the corrected
address.
Host Unknown
----- The following addresses had permanent fatal errors -----
<JDOE@SWITCHGRASS.NET>
----- Transcript of session follows -----
550 5.1.2 <JDOE@SWITCHGRASS.NET>... Host unknown (Name server:
mail.switchgrass.net.: host not found)
This means that
our mail server was
not able to locate
the mail server for
switchgrass.net (mail.switchgrass.net)
in the Internet's
domain name service
(DNS). If the target
system can't be
found in the DNS,
then our mail server
can't connect to the
remote mail server
to deliver your
message.
Most "host
unknown" errors are
caused by a typo in
the domain name part
of the intended
recipient's address,
but an increasing
number of "host
unknown" errors are
the result of trying
to reply to junk
mail (spam). This is
because the "From:"
address on junk mail
is almost always
bogus. Where the
address is typed
correctly and is a
real one, the
problem is usually a
temporary failure in
DNS.
- What you
should do:
- Confirm the
intended
recipient's
address, if
possible. Resend
your message to
the corrected
address.
Mail Quota
Exceeded
----- The following addresses had permanent fatal errors -----
<JDOE@JUNO.COM>
----- Transcript of session follows -----
... while talking to c.mx.juno.com.:
>>> RCPT To:<JDOE@JUNO.COM>
<<< 552 <JDOE@JUNO.COM>... Mail quota exceeded
554 <JDOE@JUNO.COM>... Service unavailable
Many systems
impose a quota on
the amount of disk
space each user's
mail box may use. If
a user on such a
system exceeds his
quota the mail
system refuses to
accept any more mail
for him.
The error message
returned from some
systems may look a
bit different, like
this one from
America Online:
The mail you sent could not be delivered to:
552 jdoe@aol.com has a full mailbox
Or this one from
HotMail:
<<< 552 Requested mail action aborted: exceeded storage allocation
554 5.0.0 <JDOE@HOTMAIL.COM>... Service unavailable
- What you
should do:
- Give the
intended
recipient time
to clean out
his/her mailbox,
then resend your
message.
- Note:
- comsouth.net
does impose
a 2 Meg limit on
customers'
mailboxes. If a
customer's
mailbox becomes
grossly
oversized he/she
will receive
e-mail from the
System
Administrator (
ispadmin@comsouth.net
) requesting
that it be
reduced in size.
A chronic
offender may
have his/her
incoming e-mail
blocked for a
period of time.
Message Exceeds
Maximum Size
----- The following addresses had permanent fatal errors -----
<JDOE@RESPONSE.ETRACKS.COM>
(reason: 552 5.2.3 <JDOE@comsouth.net>... Message size exceeds fixed
maximum message size (80000))
----- Transcript of session follows -----
... while talking to response.etracks.com.:
>>> MAIL From:<JDOE@comsouth.net> SIZE=222751
<<< 552 5.2.3 <JDOE@comsouth.net>... Message size exceeds fixed maximum message size (80000)
554 5.0.0 <JDOE@RESPONSE.ETRACKS.COM>... Service unavailable
On many systems
the mail server is
configured to reject
large messages. In
the past this was
usually done to
conserve disk space
on the mail server.
These days, with an
increasing number of
maturity-challenged
Internet users
thinking it is "kewl"
to clog up other
people's mailboxes
with huge junk file
attachments, it is
often used to
prevent users'
mailboxes from
overflowing their
quotas due to stupid
childish pranks.
The number in
parentheses (80000
in this example) is
not always present,
but if it is it
shows the
per-message size
limit imposed by the
remote mail system,
expressed in bytes.
- What you
should do:
- The only
solution is to
shorten the
message and try
again. In many
cases this means
deleting the
multi-megabyte
file attachment
you're trying to
send to someone
who probably
doesn't want it
anyway.
- Note:
- Normally the
comsouth.net
mail system is
configured to
reject messages
larger than 5
MB, but we
reserve the
right to change
the size limit
at any time as
required by
prevailing
conditions.
Delivery
Deferred, Will Keep
Trying
**********************************************
** THIS IS A WARNING MESSAGE ONLY **
** YOU DO NOT NEED TO RESEND YOUR MESSAGE **
**********************************************
----- The following addresses had transient non-fatal errors -----
<JDOE@SONNENSHEIN.COM>
----- Transcript of session follows -----
<JDOE@SONNENSHEIN.COM>... Deferred: Connection refused by sonnenshein.com.
Warning: message still undelivered after 4 hours
Will keep trying until message is 5 days old
If you see a
banner similar to
this at the top of a
mail delivery error
report, it means
delivery of your
message failed due
to a transient
(temporary) error.
The actual error
could be any of a
number of things.
- What you
should do:
- Do nothing!
The banner means
EXACTLY what it
says: you DO NOT
need to resend
your message.
Our mail system
will keep trying
once per hour
until delivery
succeeds or
until five days
elapse, which
ever happens
first. If after
five days the
message still
can't be
delivered,
you'll get
another error
message like the
following
example.
Message Could
Not Be Delivered For
Five Days
----- The following addresses had permanent fatal errors -----
<JDOE@SONNENSHEIN.COM>
----- Transcript of session follows -----
<JDOE@SONNENSHEIN.COM>... Deferred: Connection refused by sonnenshein.com.
Message could not be delivered for 5 days
Message will be deleted from queue
Our mail server
kept trying once an
hour for five days
but was still unable
to deliver the
message, so it gave
up trying.
- What you
should do:
- Write a
letter, make a
phone call, send
a FAX. You can
resend your e-mail
if you want to,
but if the
intended
recipient's mail
server couldn't
be reached for
five days on the
first attempt,
it probably
won't be
reachable on the
second attempt.
Sender Domain
Not Found
----- The following addresses had permanent fatal errors -----
<JDOE@AOL.COM>
----- Transcript of session follows -----
... while talking to b.mx.aol.com.:
>>> MAIL From:<JDOE@BCLP.NET>
<<< 550 <JDOE@BCLP.NET>... Sender domain not found in DNS
550 <JDOE@AOL.COM>... Service unavailable
In an attempt to
stem the flow of
spam e-mail into
their systems, many
mail systems reject
messages where the
domain name part of
the sender's address
(the part after the
"@") cannot be found
in the DNS. This is
effective against
some spam because
spammers often send
out their mass
mailings under phony
addresses.
However it also
turns away messages
from legitimate
senders whose e-mail
addresses are
incorrectly entered
in their mail
programs. In the
example above
comsouth.net
customer "jdoe"
tried to send a
message to jdoe@aol.com.
However,
comsouth.net's John
Doe mistyped the
domain name part of
his address as "bclp.net"
instead of "comsouth.net"when
he set up his mail
program. The AOL
mail system couldn't
find a domain called
"bclp.net" in the
DNS, so it rejected
the message.
This will also
block mail from
legitimate senders
who intentionally
alter their e-mail
addresses in their
own anti-spam
efforts
("jdoe@comsouth.net.NOSPAM",
for example).
- What you
should do:
- Go into your
mail program's
setup and make
sure your e-mail
address is
entered
correctly, then
resend your
message.
Possible Virus
----- The following addresses had permanent fatal errors -----
<JDOE@MEDIAONE.NET>
(reason: 553 5.0.0 Possible virus, see
http://www.symantec.com/avcenter/venc/data/w32.sircam.worm@mm.html)
----- Transcript of session follows -----
... while talking to ndmls01.mediaone.net.:
>>> DATA
<<< 553 5.0.0 Possible virus, see
http://www.symantec.com/avcenter/venc/data/w32.sircam.worm@mm.html
554 5.0.0 <JDOE@MEDIAONE.NET>... Service unavailable
Some mail systems
filter out messages
that seem to contain
viruses. If you
receive a delivery
error message
similar to the one
above, it may mean
your PC has a virus
infection and may be
sending out
virus-infected
e-mail.
- What you
should do:
- Check your
computer for
virus
infections, and
remove any that
are found.
comsouth.net
recommends that
all PCs with
Internet
connections
should have
anti-virus
software
installed. If
you already have
anti-virus
software, make
sure you know
how to use it,
make sure it is
configured to
scan files as
they are
downloaded, and
make sure you
keep its virus
description
database up to
date.
Delivery Errors
For E-Mail You Did
Not Send
You may
occasionally receive
e-mail delivery
errors for messages
you know you didn't
send. The most
common reason for
this is your address
is in someone else's
machine that is
infected with a
virus and it is
sending out as if it
is you. |
