Number 4 is awkward and shouldn't be used.
The others are correct -- but number 3 is best.
1. Reading a message is convenient for him.
2. To read a message is convenient for him.
3. It is convenient for him to read a message.
4. It is convenient his reading a message.
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Are all the sentences above grammatical?
2 answers
Thank you for using the Jiskha Homework Help Forum again. I would change #4 to "His reading a message (subject) is convenient.