Changes have been made in Git (master):

commit da97928eba951fa6d34a0d891fd821abe5f84826
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Fri May 23 15:59:34 2014 -0400

     Bug: 13208 Fix generating From: address.

  .../Core/lib/Horde/Core/ActiveSync/Driver.php      |    6 ++++--
  1 files changed, 4 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/da97928eba951fa6d34a0d891fd821abe5f84826

Hi,

with recent horde-5.2.0-git  - Horde_ActiveSync-2.16.2 (pulled from 
github) i can no longer send emails from my Android.
Android phone is connected using ActiveSync. Receiving email, syncing 
calendar, contacts, tasks and notes works fine.
When i try to send an email from Android this email stays in the 
outbox forever and the "sync circle" is turning forever too.
The eMail never reaches horde or the smtp server.

Detailed log (with Wbxml) when sending mail:
2014-05-19T14:24:08+02:00 INFO: [42509] Handling SENDMAIL command with Wbxml.
2014-05-19T14:24:08+02:00 DEBUG: [42509] I  <ComposeMail:SendMail>
2014-05-19T14:24:08+02:00 DEBUG: [42509] I   <ComposeMail:ClientId>
2014-05-19T14:24:08+02:00 DEBUG: [42509] I     SendMail-2667454925789
2014-05-19T14:24:08+02:00 DEBUG: [42509] I   </ComposeMail:ClientId>
2014-05-19T14:24:08+02:00 DEBUG: [42509] I   <ComposeMail:SaveInSentItems />
2014-05-19T14:24:08+02:00 DEBUG: [42509] I   <ComposeMail:MIME>
2014-05-19T14:24:08+02:00 DEBUG: [42509] I     Date: Mon, 19 May 2014 
14:24:07 +0200
Subject: Testmail
Message-ID: <cybh7yw6yxoyfnjvu9s5qxrb.1400502247419@email.android.com>
From: "User" <user@domain.tld>
To: user@domain.tld
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64

VGVzdA==

2014-05-19T14:24:08+02:00 DEBUG: [42509] I   </ComposeMail:MIME>
2014-05-19T14:24:08+02:00 DEBUG: [42509] I  </ComposeMail:SendMail>
2014-05-19T14:24:08+02:00 ERR: Address is missing domain.

Identity is correctly set up.
For our setup every default identity is in the form
     lastname, firstname
  -> e.g. Pulz, Joerg

In the Full name field of the identity: Pulz, Joerg
In the default e-mail address field: Joerg.Pulz@frm2.tum.de

The Horde WebUI displays this correct in the upper right as
     "lastname, firstname" <email address>
  -> e.g. "Pulz, Joerg" <Joerg.Pulz@frm2.tum.de>

With some additional debug in Horde_Core_ActiveSync_Driver::sendMail() 
i tracked this down and think it's most probably commit 
07bdf1e2734fbf8dc876c896315375d13c0311a6.

When i try to send an email using ActiveSync i get the following 
headers from the device
     ["from"]=>
     array(2) {
       ["h"]=>
       string(4) "From"
       ["v"]=>
       string(33) ""Pulz, Joerg" <jpulz@frm2.tum.de>"
     }
     ["to"]=>
     array(2) {
       ["h"]=>
       string(2) "To"
       ["v"]=>
       string(22) "Joerg.Pulz@frm2.tum.de"
     }

Right after this part of code in Horde_Core_ActiveSync_Driver::sendMail()
    1855         // Always add From: since we allow selecting the identity.
    1856         $headers->removeHeader('From');
    1857         $headers->addHeader('From', $this->_getIdentityFromAddress());

i get the following headers
     ["to"]=>
     array(2) {
       ["h"]=>
       string(2) "To"
       ["v"]=>
       string(22) "Joerg.Pulz@frm2.tum.de"
     }
     array(2) {
       ["h"]=>
       string(4) "From"
       ["v"]=>
       string(36) "Pulz, Joerg <Joerg.Pulz@frm2.tum.de>"
     }

As you can see, the double quotes around the fullname are missing, 
which at the end leads to my error "Address is missing domain".

For now i just modified 
Horde_Core_ActiveSync_Driver::_getIdentityFromAddress() to return 
explicit double quotes around the fullname

     return '"' . $name . '" <' . $from_addr . '>';

instead of

     return $name . ' <' . $from_addr . '>';

This solves my problem for now and i can send email using ActiveSync, 
but i think this is absolutely a hack and no clean solution as it's 
not required for fullnames that don't contain a comma.

A better and official fix for this problem is much appreciated.