You can install or enable some PHP extensions which will make SquirrelMail
functionality run faster. SquirrelMail uses gettext functions for translations.
If PHP gettext extension is not present, the interface switches to slower
internal gettext implementation.
If you use CRAM-MD5 or DIGEST-MD5 authentication methods, SquirrelMail can use
PHP mhash functions. If PHP mhash extension is not present, interface uses own
In some cases SquirrelMail can take advantage of PHP recode or iconv
functions. These functions can be used to speedup decoding of CJK charsets.
If the IMAP server supports the IMAP extension SORT (most mainstream servers do)
enable this feature in SquirrelMail's configuration. In general, always enable
this option if your server supports it since it's way faster than sorting in
SquirrelMail, and may prevent problems for end users with very large mailboxes.
When not using server-side sorting, these end users may get an empty page upon
viewing the large mailbox, because the PHP sorting times out. It'll vary by
machine speed, but it has been reported that when viewing a folder containing
circa 17,000 mails, the initial viewing delays can decrease from around 35
seconds to 4 seconds.
The only case when server-side sorting causes problems in SquirrelMail is when
the IMAP server doesn't support the character set used by the translation
selected in SquirrelMail. SquirrelMail can use more than 15 character sets in
server-side sorting and threading commands. Courier IMAP server only supports
them when compiled with the --enable-unicode option. Cyrus IMAP (v.2.2.12)
doesn't support some of the multibyte character sets used by SquirrelMail.
SquirrelMail also allows using server-side threading if the IMAP server supports
it. This option offers the end users to view the message list in a thread view.
Threaded sorting requires more system resources and you should enable it only if
you want to provide such an option to end users.
Enabling the extensions
To find out if the IMAP server supports server-side sorting and threading,
telnet to it and ask:
> telnet imapserver.example.com imap
* CAPABILITY IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE AUTH=PLAIN STARTTLS
1 OK CAPABILITY completed
The SORT and THREAD capabilities indicates that this server supports these
extensions. Next step is to configure SquirrelMail to use them.
4. General Options
10. Allow server thread sort: false
11. Allow server-side sorting: false
SquirrelMail 1.5.1 introduces some changes when it comes to sorting and
threading. Sorting and threading is used by default, if the IMAP server supports
it (according to the IMAP server's CAPABILITY response). It is, however,
possible to manually override that, thus disabling them, in SquirrelMail's
4. General Options
10. Disable server thread sort: false
11. Disable server-side sorting: false
The default Unix mailbox format is slower than other formats and can increase server
loads when used with bigger mail folders. If you use UW IMAP server, you should
try switching to mbx mailbox format. Maildir mailboxes have higher bottlenecks
than formats that store entire mail folder in one file.
Mail filtering, i.e. deleting mails or putting them in selected folders based on
criteria, isn't a must have mail system feature, but it sure is one of those
nice to have features that the end users might require.
To avoid negative performance impact as much as possible, systems providing mail
filtering should do so by using a server side application. The SquirrelMail
package includes the Filter plugin, but it should be the last resort when other
means of filtering can't be provided. The plugin is implemented in PHP and works
only when users actively log in to their mail accounts, making the display of
the folders slower (typically when logging in, and especially for accounts with
a large amount of mail) or, at worst, produce errors thus preventing the use of
some accounts completely. Server side filtering, performed by applications such
Maildrop, or any application
Sieve; provide more
options, work even when users do not actively log into their accounts, and are
much faster and more efficient.
SquirrelMail frontends for server side filtering applications are found at the
Filters & Spam section of the plugin pages.
A caching IMAP proxy server can vastly improve SquirrelMail performance by
cutting down on the number of times you have to create a new connection to the
IMAP server. It keeps server connections alive for reuse avoiding a new IMAP
connection for each SquirrelMail transaction. Install the proxy at the web
server, configure SquirrelMail to connect to the proxy (localhost), and
configure the proxy to connect to the IMAP server. A side benefit is your logs
aren't full of IMAP logins.
IMAP Proxy is a caching IMAP proxy
server known to be working well in various SquirrelMail installations. The
latest version allows log levels to be configured at runtime from the
configuration file. It's free, open source software and runs on various
A PHP cache is a tool that might speed up PHP scripts. The general idea is to
check if a PHP script is modified since it was cached, and use the cached copy
if it wasn't. If the script is new or modifed, it's compiled and cached. The
benefit is that using precomplied, cached copies of the script are quicker then
compiling the script every time it's requested. Here are some examples of
products to try:
Alternative PHP Cache is a
"free, open, and robust framework for caching and optimizing PHP intermediate
code". It's released under the PHP License.
eAccelerator is a fork of the old,
Turck MMCache for PHP project. It's described as a "free open-source
PHP accelerator, optimizer, encoder and dynamic content cache", and is released
under the GNU LGPL.
PHP Accelerator is an
"easily installed PHP Zend engine extension that provides a PHP cache, and is
capable of delivering a substantial acceleration of PHP scripts without
requiring any script changes, loss of dynamic content, or other application
compromises". There is no official license for PHPA, and it's free for use.
Zend Optimizer is a "free application that runs the files encoded by the Zend
Guard, while enhancing the performance of PHP applications." It's released under
the Zend License Agreement.
Sometimes the speed of the server is perceived to be terribly slow, but it is
the cause of the modem speed or bandwidth at some intermediate server. To cut
down on the amount of traffic generated from the server, you could compress web
pages or condense them by removing excess garbage. Keep in mind that this will
put a little more load on your server, but it is practically nothing when
compared to your IMAP server and SquirrelMail.
These solutions only compress the output to clients that support it, so you
don't need to worry about corrupting data to some older browsers by enabling any
of the options listed below. They are listed in order of preference.
Only implement one or else you might get some weird problems.
Configure the web server to compress the web pages (and maybe images).
The module mod_deflate is part of Apache since 2.0 and there's also
a third party module for Apache called mod_gzip.
PHP can also compress all PHP pages sent out by setting the
output_handler to ob_gzhandler, or enable
zlib.output_compression in php.ini.
SquirrelMail has the
Gzip Compressed Output plugin that enables compression of output
in the same way that PHP does (see above), but only for SquirrelMail.
This refers to cleaning the HTML and removing unnecessary garbage in an effort
to send as little to the client without actually changing the structure of the
web page. Usually white space (extra spaces and new lines) are condensed into
one, comments are removed, and sometimes HTML tags will be changed to be more
Unfortunately the SquirrelMail Project Team doesn't know of a semi-standard
module or PHP extension that does this, but we'd like to be informed if you find