postal - program to test SMTP mail server throughput.
postal [-m maximum-message-size] [-M minimum-message-size] [-t threads]
[-c messages-per-connection] [-r messages-per-minute] [-s
ssl-percentage] [-l local-address] [-a] [-b [no]netscape] [-[z|Z]
debug-file] [-f sender-file] smtp-server user-list-filename
This manual page documents briefly the postal, program.
It is designed to test the performance of SMTP email servers by sending
random messages to the specified server as fast as possible.
The smtp-server parameter specifies the IP address or name of the mail
server that the mail is to be sent to. Mail sent by Postal will not
use MX records, this is to allow testing outbound relays etc. If you
want to specify a port other than port 25 then enclose the host address
in square brackets and have the port address immidiately following. If
you want a DNS lookup for every connection (for testing round-robin
DNS) then immediately preceed the host address with a ’+’ character.
To specify multiple servers for round-robin use then seperate the
addresses with commas. Note that localhost is used for connecting to
the same machine.
The user-list-filename is the name of a file which contains a list of
user’s email addresses. This can be just user-names or fully qualified
email addresses. Whatever you specify will be sent exactly in the SMTP
protocol so make sure you do whatever is appropriate. If unsure then
use fully qualified addresses (IE firstname.lastname@example.org).
The sender-file contains a list of users that will be in the From:
field and envelope sender of the messages. If it is not specified then
the user-list-filename will be used for the sender list.
The maximum-message-size indicates the size in Kilobytes that will be
the maximum size of the message body. The size of each message body
will be a random number between 0 and the maximum size. Specify "0" if
you want just headers to test the connection rate. The default value
The threads parameter is the number of threads that should be created
to attempt seperate connections. A well configured mail server won’t
accept an unlimited number of connections so make sure you don’t
specify a number larger than the number your mail server is configured
to handle. Also for sensible results make sure that you don’t use
enough to make your server thrash as the results won’t be
representative of real-world use. The default value is 1, this default
is not suitable for real tests, it’s just for testing your
configuration. If you specify multiple server addresses for
round-robin use then this number of threads will be created per server,
IE 4 servers and -p5 will give 20 threads total.
The messages-per-connection parameter is for sending more than one
message per SMTP connection. The default value is "1". A value of -1
means to send an indefinate number of messages on one connection (~4
billion). If a value > 1 is specified then the number sent on each
connection is a random number between 1 and the number specified. For
simulating a mail server connected directly to the net use a value of 2
or 3. For simulating a mail server connected to a front-end relay use
a large number. For testing for bugs in your mail server use the value
0 and leave it running for a week. ;) A value of 0 means to
disconnect without sending any messages. Good for testing a
The max-messages-per-minute parameter is for limiting the throughput of
the program. This is designed to be used when you want to test the
performance of other programs when the system is under load. The
default is effectively 24000 messages per minute.
The local-address parameter specifies which local IP address(es) are
used to make the outbound connections. Specified in the same way as
the remote address. This is good for testing LocalDirectors or other
devices that perform differently depending on which source IP address
The -a command turns on all logging. All message data received will be
logged. This will make it slow and it may not be able to saturate a
fast Ethernet link...
The -b switch allows you to specify breakage strings. Currently the
only option is for Netscape mail server which strips spaces from the
start of subject lines. -b netscape means to avoid leading spaces on
subject fields to not break Netscape. -b nonetscape means to always
put extra space to test for the bug in Netscape and similar products.
Some people say that the RFCs are open to interpretation on this issue,
I am interested to see whether anyone else interprets it the way that
The -s switch specifies the percentage of connections which are to use
TLS AKA SSL. Use 0 for no SSL, or 100 for always SSL, or any number in
between. Default is 0.
The -z switch allows you to specify a debugging file base. From this
base one file is created for each thread (with a ’:’ and the thread
number appended), each file is used to log all IO performed by that
thread for debugging purposes.
The -Z switch is the same but creates a separate file for each
connection as well with an attitional ’:’ appended followed by the
When testing mail servers please use domains defined in http://www.rfc-
editor.org/rfc/rfc2606.txt - example.com, example.net, and example.org
are all good options. Please don’t use anything related to a valid
name, that will cause pain for you and others on the net.
0 No Error
1 Bad Parameters
2 System Error, lack of memory or some other resource
This program, it’s manual page, and the Debian package were written by
Russell Coker <email@example.com>.
The source is available from http://doc.coker.com.au/projects/postal/ .
See http://etbe.coker.com.au/category/benchmark for further