How can I validate if a MimeMessage is valid and can be delivered?

[ramonsmits]

How can I validate if a MimeMessage is valid and has a minimum set of required properties set for it to be delivered?

[jstedfast]

RFCs like rfc5322 suggest that the only required headers are From, Date and To, Cc, and/or Bcc (in other words, you need the sender, date, and 1 or more recipients to be defined). Older versions of the specification seemed to indicate that Message-Id should be present as well.

MimeKit automatically sets a Date and Message-Id header when you create a new MimeMessage.