Why is DKIM not valid?

Question

postfix

Tell me please. I send a letter through the mail () function in php - DKIM is not valid, but when sending through the terminal, everything is ok. Why is that? If you need any information, please let me know and I'll add it.

Answer 1

Perhaps you do not form, but sign one of the required headers, Date: or Message-ID:, which is then added by the server after the signing, or form lines that are too long and break during transmission. Show the header of the letter with the wrong signature from the external server.