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When you say you can only send them a link - do you mean after you send one, the receiver receives a link to access it?
If so, thats more to do with the person receiving the MMS than the person sending it. If you phones sends it, then you are set up correctly.
Some phones are not great at receiving them though for various reasons.
With the advance of other platforms to send MMS style content for free, MMS have not really been a priorty for most network globally. Where as once we would pay 32 cent or whatever it was to send a simple picture, now most simply use whatsapp, or replace their text message application with something like Signal which does all this over the internet and free of charge.
+1 for using other apps
Also I noticed is that some people dont have their Mobile data enabled when sending MMS, MMS can only be sent over Mobile Data
Our apologies for the delay in responding to your query. We have received a high volume of queries and are working through our messages in the order they have come in. You may be receiving a link as the person you are sending it to does not have a smartphone, therefore they would be unable to receive the picture on the handset itself and they would need to log into their My Vodafone account to view it. ~Ailís