I see it under the headers. But not under the SmtpapiHeader. Is that correct?
[headers] => Array
(
[X-Mailer] => Postman SMTP 1.7.2 for WordPress (https://wordpress.org/plugins/postman-smtp/)
[X-SMTPAPI] => {“category”: [“WordPress”]}
[Content-Type] => multipart/alternative
[Sender] =>
)
[smtpapi] => SmtpapiHeader Object
(
[to] => Array
(
)
[sub] => Array
(
)
[unique_args] => Array
(
)
[category] => Array
(
)
[section] => Array
(
)
[filters] => Array
(
)
[send_at] =>
[send_each_at] => Array
(
)
[asm_group_id] =>
[ipPool] =>
)
