When i try to send or answer incoming mail, even if the sent mail is totally empty, or unchanged, if received, its blocked with the comment “the message has been blocked for containing SPAM-like characteristics”.
Are you using signatures? If so, can you disable them and try again?
If not, a server may block a message that has no content. That is understandable.
But for replies, if your server is blocking the message because of spam-like characteristics, you will need to contact them and ask for assistance. Hopefully they can elaborate on what those characteristics are that causes them to reject the message.