=== SanitizeMimeMessageId Mailet

Some email clients, such as Outlook for Android, may send emails **without a `Message-ID` header**.

== Why is this needed?
 The absence of the `Message-ID` header can cause emails to be rejected by downstream mail servers,
 as required by RFC 5322 specifications. For example, Gmail rejects messages without this header with
 an error like the following:
 550-5.7.1 [IP] Messages missing a valid Message-ID header are not
 550-5.7.1 accepted. For more information, go to
 550-5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant and review
 550 5.7.1 RFC 5322 specifications.

To mitigate this, the `SanitizeMimeMessageId` mailet will automatically add a `Message-ID` to emails **that lack one**.

== Configuration

You can configure it simply by adding the following in your `mailetcontainer.xml` file:

....
<mailet match="All" class="SanitizeMimeMessageId"/>
....

== Behavior

- If a `Message-ID` header already exists: nothing is done.
- If the header is missing: a new one is generated and added.

