I receive many Islamic messages. I forward them to my contacts, especially if it implies to them. If 1 of my contact blocked me simply the message relates to them and never wants to communicate with me, is he sinful for behaving in an ill manner?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

That person is not sinful simply because he has blocked you because of the message you sent to him, but he should not have blocked you because of that.

If the content of that message warned him of a deficiency in him or negligence, then he should benefit from it, correct his mistake, and abide by the truth because abiding by the truth is a virtue.

As far as you are concerned, if you predominantly think that the method of advice and guidance you used might have provoked that person, then perhaps it is more appropriate to look for another method for advice which would be more suitable and which is more likely to be accepted.

Allah knows best.