We do know the importance of having options on your phone that meets your needs, sloppyseconded. We are here to help. Researching the resizing concern for MMS, we are sad to say that there is no option to turn that off. It is depended on the phone model itself.
Regarding the larger files not sending, this can also be a limitation of the phone as well. Have you tried connecting to Wi-Fi to send a larger MMS or file? Have you tried sending a larger files to another user with a Galaxy S8 using Message+?
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