What's the matter that Xiaomi can't get resources from SMS pictures?

This has something to do with mobile or Unicom networks. When we accept short message pictures (so-called MMS), the transmission intersection of operators will change. This is not a GPRS portal. I have forgotten what the entrance is. Then, this unique receiving entrance is related to the strength of the local signal, and the stronger the signal, the easier it is to accept. However, now that the 4G network has been upgraded, I think there are two reasons for not accepting it: First, the information has expired; Second, the local network signal coverage is weak.