get_first_named_header_value
Gets the first header whose name matches NAME, decode it to UTF-8 and return
it.
Returns nil if no matching header could be found.
Since: Version 2026.04.09-ea3b2a9b
The functionality described in this section requires version 2026.04.09-ea3b2a9b of KumoMTA, or a more recent version.
When the structured header parser fails (for example, due to non-conforming
header content), this method now falls back to returning the raw header value
rather than raising an error. This improves resilience when processing
messages with headers that do not strictly conform to the RFCs.
The same fallback applies to get_all_named_header_values and get_all_headers.