Mutable builder for Email; usually used through emailBuilder.
The Date header; the time of rendering is used if null.
Date
null
The Message-ID without angle brackets; generated from the sender's domain if null.
Message-ID
Attach a file.
Embed a file that the HTML body references via cid:<contentId>.
cid:<contentId>
Set the sender, either john@example.com or John <john@example.com> if name is null.
john@example.com
John <john@example.com>
Add a custom header, e.g. List-Unsubscribe.
List-Unsubscribe