What this check looks at
JoltMx reads the stored message's headers and checks them for the basics every well-behaved mailer gets right:
- From - required by RFC 5322; mail without one is rejected almost everywhere.
- Message-ID - present, and in the standard
<unique@domain>form. - Date - present, parseable, and not wildly out of sync with the real delivery time.
- Subject - present (empty subjects score poorly).
- Reply-To - flagged when it points at a different domain than From (a phishing pattern).
- List-Unsubscribe - rewarded when present; nudges you toward one-click support.
Why it matters
These headers cost nothing to set and their absence is a strong "this was generated by a script" signal. A badly skewed Date makes mail look forged and breaks threading. And for bulk senders, a working List-Unsubscribe (with one-click) is now expected by Gmail and Yahoo.
How the diagnostic grades it
| Result | Severity | What it means |
|---|---|---|
| Header hygiene | Pass | From, Date, Message-ID and Subject are all present and well-formed. |
| List-Unsubscribe present | Pass | Good for bulk mail; add List-Unsubscribe-Post for one-click. |
| Missing From header | Critical | Required by RFC 5322; rejected almost everywhere. |
| Missing Message-ID | Warning | A common spam-filter signal. Configure your server to add one. |
| Missing / unparseable Date | Warning | Filters penalise mail without a valid Date. |
| Date header is skewed | Warning | More than an hour off real time - sync the server clock (NTP). |
| Malformed Message-ID | Info | Not in the standard <unique@domain> form. |
| Empty Subject | Info | Not an error, but empty subjects score poorly. |
| Reply-To uses a different domain | Info | Legitimate for some workflows, but also a phishing pattern. |
How to fix it
- Use real mail software (or a reputable provider) that sets
From,DateandMessage-IDautomatically. - Keep the sending server's clock synced with NTP.
- For bulk mail, add
List-UnsubscribeandList-Unsubscribe-Post: List-Unsubscribe=One-Click.