Thanks for the hint, upgraded my debian squeez to dotdeb PHP packages 
(5.4) and now it works.

Looking at this more... this comment is a Duplicate of #13342.

Still don't know if this is the root of the issue reported by the OP though.

Is anybody here that sees the issue using PHP 5.3.3?

We had the same or very similar problem - and we developed a hotfix 
for our special case. This could not be the final solution but its a 
workaround. I think we have do investigate the reason why ...

I found that horde/services/portal/smartmobile.php might produce a 
broken link if the smartmobile link contains a '#' or something like 
this. The imp initial_page is 
/horde/imp/smartmobile.php#mailbox?mbox=SU5CT1g and after building a 
Horde_Core_Smartmobile_Url from this it has the value of just 
/horde/#mailbox?mbox=SU5CT1g - no 'imp' nor 'smartmobile.php' 
contained in the resulting link.

This broken link causing  302 Errors until we get the error message of 
to many recursive redirections.

The patch attached solved the Problem for us.  Probably this is caused 
by our special configuration here - or it is caused by the constructor 
of the Horde_Core_Smartmobile_Url

[root@horde-dev horde/services/portal]# diff smartmobile.o.php smartmobile.php
27a28,29
29c31,32
<         new 
Horde_Core_Smartmobile_Url(Horde::url($registry->getInitialPage($app))),
---

No.  The changes mentioned in this ticket were in Horde_Core.  So I 
have no idea whether you have updated that to the newest release.
Nope.  At this point, you are probably going to have to trace the 
cause of the issue yourself locally.

Thanks! :)
Sorry, I was too tired:
The changes of the commit are available in my stadard installation, so 
I assume, the changes are already published in a stable release. 
Unfortunately the error still exists.

Was someone else able to repoduce the error with the latest iOS release?

Torben

Congratulations!
This issue has nothing to do with ActiveSync. Are you replying to the 
correct ticket?

Hm, neither the horde log nor the apache log throws an error.

However, horde thros an endless list of "EMERG: HORDE User is not 
authorized [pid 18167 on line 1546 of 
"/usr/share/php/Horde/Registry.php"]
" errors - but I do not know what they mean..

Michael, sorry for the delay, my child was born.

Is the mentioned commit included in Activesync 2.16.11?

If yes,it does not help, it still does not work with iOS 7.1.2.
I'll look in the logfiles to get a clue..

Torben

Maybe this fixes?

commit 61dff1f7855ab7243656ab71d776bdbec3764e9f
Author: Michael M Slusarz <slusarz at horde.org>
Date:   Tue Jul 8 15:27:24 2014 -0600

     [mms] Sanity checking in case smartmobile URL contains anchor 
that doesn't exist on the page.

  framework/Core/js/smartmobile.js |   11 +++++++++--
  framework/Core/package.xml       |    4 ++--
  2 files changed, 11 insertions(+), 4 deletions(-)

http://github.com/horde/horde/commit/61dff1f7855ab7243656ab71d776bdbec3764e9f

Can't reproduce either, although I only have Android devices to test on.

with desktop browser it works as expected.

I'll check it at the weekend..

Works fine with 7.1.1. You probably have some JS error. Try with a 
desktop browser and check the console log.

I tested with iOS 7.1.2 (current stable)

"clicking" on the webmail app just shows the loading progress bar for 
some seconds but nothing happens afterwards..

Cannot reproduce

After upgrading to latest horde/imp RC, it is possible to log into 
horde via smartphone, but "clicking" on the webmail link does not work.