Enquiries going to SPAM

My web host has come back to me with a spam report.

• 0.8 PHP_MAILER No description available.
• 0.8 HEADER_FROM_DIFFERENT_DOMAINS From and EnvelopeFrom 2nd level mail domains are different
• -0.0 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain
• 0.3 HTML_MESSAGE BODY: HTML included in message
• 0.7 MIME_HTML_ONLY BODY: Message only has text/html MIME parts
• 2.0 BAYES_50 BODY: Bayes spam probability is 40 to 60% [score: 0.4385]
• 0.4 HTML_MIME_NO_HTML_TAG HTML-only message, but there is no HTML tag
• 2.1 FREEMAIL_FORGED_REPLYTO Freemail in Reply-To, but not From
• 1.0 TO_NO_BRKTS_HTML_ONLY To: lacks brackets and HTML only

But the main one is that the email forges the sender address ( to be the user)
There’s no plain test part, so it gets a score for that
Also the to address should be wrapped in <>
All those push the score (8,1) up to above the SPAM threshold (which is 6.2)

Can you let me know where the sender address is set so I can at least change this stuff?