Help My contacts are not receiving my messages From my cell phone

[Android Question]

Can you tell me why some of my contacts are not receiving my messages

 

[Hadron]

Not without more information.

What do these contacts have in common which differs from those who do receive the messages? Can you receive messages from them? Have you recently changed phone/OS/network, and did the problem start then? If not, what changed shortly before the problem started? Is this SMS, MMS, both, or some internet-based message app? This is the sort of information which will help us work out what your problem is.