OK. It seems the problem came from mod_dosevasive and is not related to Horde.

Maybe IMP has some problems at times that make it look like a little DOS.



So It's not a bug, but maybe something to watch for (improve) and 
maybe that's something that could be added to the FAQ?

Here is some info about the browser

The user clicked the problem report link from the following location:

https://website.com/webmail/imp/compose.php?thismailbox=INBOX&nocache=7hyc68ll2nk8

and is using the following browser:

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)

I don't have the yellow warning icon telling me that there are errors, 
so I guess there are none.



Here is how to make it display a 404 almost every time.



-create a new message,

-make sure that the charset is at UTF-8,

-click on the addressbook icon,

-select 5 email addresses and put them in bcc

-click send



I get a 404 almost every time. I've tried in American English and in 
French with the Blue and White theme.

How about javascript errors? If you can't give us anything to start 
with, we can't really help.

That's part of the problem, there is nothing significative in the 
logs. No indication of a 404 or a ssl error.



Also, it looks like as if compose.php doesn't have time to send 
anything. It happens right after you release the submit button.

Check your web server and php log files.

Also, IE tells me this about the secure connection:



TLS 1.0, RC4 with 128 bit encryption (High); RSA with 1024 bit exchange

Yes, I use HTTPS only.

Here is my SSL config in Apache



SSLCipherSuite 
ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL



I also have this in place:

SetEnvIf User-Agent ".*MSIE.*" \

          nokeepalive ssl-unclean-shutdown \

          downgrade-1.0 force-response-1.0

Are using HTTPS and have you disabled the known bad IE ciphers in 
apache's config file - 
http://www.horde.org/faq/admin/trouble/index.php#t47

My users forced to use Internet Explorer 6 get a "The page cannot be 
displayed" message at random when trying to send emails.

This is very annoying because all their work is lost.

Firefox has no problems.

I don't see anything relevant in the logs (Apache, ssl, php)



FreeBSD 5.4

Apache 1.33

PHP 4.4.0



'./configure' '--with-apxs' '--disable-ipv6' 
'--with-openssl=/usr/local' '--with-kerberos' '--with-zlib' 
'--with-curl=/usr/local' '--with-gd=/usr/local' 
'--with-jpeg-dir=/usr/local' '--with-png-dir=/usr/local' 
'--enable-gd-native-ttf' '--with-ttf' '--with-freetype-dir=/usr/local' 
'--with-gettext' '--with-mcrypt' '--with-mhash' 
'--with-mysql=/usr/local/mysql' '--with-pear' '--with-dom' 
'--with-dom-xslt' '--with-dom-exslt' '--with-zip' '--enable-bcmath' 
'--enable-calendar' '--enable-ftp' '--enable-magic-quotes' 
'--enable-sockets' '--enable-track-vars' '--with-iconv=/usr/local' 
'--with-imap' '--with-imap-ssl' '--with-bz2' '--enable-mbstring=all'



IMAP c-Client Version         2004

SSL Support         enabled





I've found some old PHP bug report from 2002, but it's shown as fixed 
and I don't have any segfaults in the logs.