[horde] Server side email searches with ActiveSync not working

[Sebastian Arcus]

I am struggling to get server side email searches working with ActiveSync.

My setup is:

Lighttpd 1.4.49
Dovecot 2.2.33
Exim 4.90
PHP 5.6.35
Postgresql 9.2.24
Horde 5.2.17

I have tested imap searches through Thunderbird (there is an option "run 
search on server) and it is working fine and fast. I assume this means 
Dovecot is configured correctly and can do imap searches?

I have tested the Horde email searches on an iPhone 5S with iOS 11.2.6 
and a Jolla phone with Sailfish 2.1. Both of them have email configured 
in ActiveSync mode. On both of them, if I force them to search on the 
server only, they sit there saying "searching" for a few minutes, and 
then return no results (and no error either).

On the server side, I can see the command being sent by the device to 
Horde in the individual device ActiveSync log (I've removed the 
timestamps for brevity):

[12466]INFO: ----------SEARCH request received for user 
myusername at mydomain.com
[12466][2018-04-16T15:27:38+01:00] INFO: ----------Request being handled 
for device: JP359745050349650, Supporting protocol version: 14.0, Using 
Horde_ActiveSync v2.39.2
[12466] I: <Search:Search>
[12466] I:  <Search:Store>
[12466] I:   <Search:Name>
[12466] I:     Mailbox
[12466] I:   </Search:Name>
[12466] I:   <Search:Query>
[12466] I:    <Search:And>
[12466] I:     <Search:FreeText>
[12466] I:       dea
[12466] I:     </Search:FreeText>
[12466] I:     <FolderType>
[12466] I:       Email
[12466] I:     </FolderType>
[12466] I:    </Search:And>
[12466] I:   </Search:Query>
[12466] I:   <Search:Options>
[12466] I:    <Search:Range>
[12466] I:      0-100
[12466] I:    </Search:Range>
[12466] I:    <Search:DeepTraversal />
[12466] I:    <Search:RebuildResults />
[12466] I:    <AirSyncBase:BodyPreference>
[12466] I:     <AirSyncBase:Type>
[12466] I:       2
[12466] I:     </AirSyncBase:Type>
[12466] I:     <AirSyncBase:AllOrNone>
[12466] I:       1
[12466] I:     </AirSyncBase:AllOrNone>
[12466] I:     <AirSyncBase:Preview>
[12466] I:       255
[12466] I:     </AirSyncBase:Preview>
[12466] I:    </AirSyncBase:BodyPreference>
[12466] I:    <MIMESupport>
[12466] I:      0
[12466] I:    </MIMESupport>
[12466] I:   </Search:Options>
[12466] I:  </Search:Store>
[12466] I: </Search:Search>


But I just can't be sure it is actually passed to Dovecot - at least I 
can't see anything in the Dovecot logs to indicate that.

Are there any other settings needed for ActiveSync server side email 
searches to work? Can I troubleshoot this further, or look in any other 
logs?

Any advice much appreciated.