Share your experience!
Hi!
I am new to this forum 
All day today I have been having trouble sending MMS [picture messages] messages. I cannot send any photos to anyone. It immediately says "could not send" with the red SMS notification. I have tried turning on and off the phone repeatedly, turning on and off my WIFI, and nothing has worked. I even tried sending myself a picture and it fails. The only thing I can think of is I had my phone on my STAMINA mode from last night to this morning for the first time. I tried the mode because I kept getting a notification saying I should use it, and I tried it. But then this morning I couldn't send any MMS this morning. I took it off and it still won't allow me to send any MMS.
How can I fix this? I send a lot of MMS and I am pretty shocked at this.
Settigs > xperia > internet settings
also make sure that your data is on (not wifi)
Hi there, thank you for replying. I have been sitting here looking for the "internet settings" under my settings and I cannot find that 
When I go under settings, I see the following:
WIRELESS & NETWORKS
Wi-Fi
Bluetooth
Data Useage
Xperia Connectivity
More..
DEVICE
Personalization
Call Settings
Sound
Display
Storage
Power Management
Apps
PERSONAL
Location services
Security
Language & Input
Backup & reset
Setup Guide
ACCOUNTS
which lists my apps
SYSTEM
Date & Time
Accessibility
ABout Phone
Am I missing it? Or not clicking under the right option? I have looked under several of them and cannot find "internet settings." I asked a friend who has the Z1S to check as well and they're not seeing that option either.
My bad
Settings > more > Internet settings
if that doesn't work then
settings > more > mobile networks > access point names > Menu > add New > enter the settings manually > menu > save
Hi there, thanks for such a quick reply. I am not too tech savvy when it comes to settings, so please bare with me 
I am not seeing this first option you gave: Settings > more > Internet settings
And this second one,
settings > more > mobile networks > access point names > Menu > add New > enter the settings manually > menu > save
Which network/carrier do you have? and which country ?
I have T-Mobile and I am in the US
Name:T-Mobile.
Apn:fast.t-mobile.com
proxy:216.155.165.050
port:8080
MMSC:http:mms.msg.eng.t-mobile.com/mms/wapenc
MMS port:8080
MCC:310
MNC:260
APN protocol:IPv4
APN roaming protocol:IPv4
Menu > Save > then Menu > add New
Name: T-Mobile GPRS
APN:epc.tmobile.com
MCC:310
MNC:260
APN protocol:IPv4
APN roaming protocol:IPv4
The Dutch site has a help for setting up mms settings. I cannot find that on usa site.
T-Mobile has a service to send all the correct settings as sms, so that you configure it with one press on a message, but this seems unavailable on Sony devices (I think only on apple/samsung/blackberry).
I cannot find a mms settings help on your region:
support.t-mobile.com/community/phones-tablets-devices/android/sony-xperia-z1s/content
But i do have a link from the Dutch site. But their config is different from what uliwooly wrote above.(possibly because it's for Dutch users)
I'll deeplink to start of mms settings, step by step. (volgende = next in Dutch) it has a good to understand animation:
www.t-mobile.nl/toestelhulp#/sony/c6903-xperia-z1/mms/usecase/handmatig-instellen/2
(use googletranslate if nessesary (Dutch to English)
Best way is to call t-mobile in your country and verify the settings of Uliwooly above this posting.