Contains the header of each message. The headers are unfolded, which means that each header takes one line, regardless of how it was in the original raw message. They're also decoded: quoted printable and base64 content is converted to native characters when possible.
> Columns
mail_id: integer, unique
Unique internal identifier of the message. This is a foreign key
to mail.mail_id.
lines: text
The contents of the header.
header_size: integer
The size of the header in bytes. Should be equal to length(lines).
> Size
One row per message in the database.