Hello!
i’ve a similar problem. I’m using Posteo for syncing contacts and calendar.
When i change/add a contact photo on my old Smartphone (Cyanogenmod11), on my new Smartphone (Android 5.1) or on my Tablet (Android 5.0) it doesn’t appear at Thunderbird or the other devices. But at Posteo i can see the changed photo. So the pictures seems to “leave” the Android Device.
When i change/add a picture in Posteo it appears at the Android Devices but not at Thunderbird (the old pictures disappears simply).
The only way to have a correct synchronization is to change the pictures in Thunderbird (Version 38.4.0 with SOGo Connector 31.0.1. I also use MoreFunctionsForAddressbook 0.7.3). Then i see the changed Pictures on the android devices and at the Posteo Website.
So i dont know exactly where the fault could be.
I contacted the Posteo Support weeks ago but until now i didn’t get a answer.
Maybe anybody has a idea?
At gitlab i couldnt post a snippet (Error: 404 The page you’re looking for could not be found) so i post my Debug-Info here. When i should do it otherwise, please let me know.
SOFTWARE INFORMATION
DAVdroid version: 0.9.1.2 (86) Fri Jan 01 14:07:08 MEZ 2016
Installed from: com.android.vending
JB Workaround installed: no
CONFIGURATION
System-wide synchronization: automatically
Account: Posteo
Address book sync. interval: 1440 min
Calendar sync. interval: 1440 min
OpenTasks sync. interval: —
SYSTEM INFORMATION
Android version: 5.1 (r4275.1_FP2_gms36_1.1.7)
Device: Fairphone FP2 (FP2)
Thanks!
So the pictures seems to “leave” the Android Device.
It really seems like this is a 3rd-party problem.
To be sure, please enable verbose logs, upload a photo and post the logs of the upload process here.
PS: Thanks for the hint – GitLab snippets require login, I have adapted the instructions.
PS 2: Still waiting for my FP 2 
Thanks for the quick answer.
Made a photo, added it at a contact and uploaded it.
Even when i’m logged in, i cant use GitLab because of the Error.
I posted the verbose log here now:
https://piratenpad.org/p/Q5RkR3QQVq
But it seems, like it is a problem with the Posteo Server right?
@neolovich said:
Even when i’m logged in, i cant use GitLab because of the Error.
Really? Strange, maybe only project owners can post Snippets. I’ll check that.
But it seems, like it is a problem with the Posteo Server right?
At least, I can’t see anything wrong with the photo upload. So I guess this is a problem of Posteo and/or your other clients.
Thanks for the answer 
I’ll contact Posteo again.