MessageId are not properly initialized when passed as Header in MimeMessage constructor

[ivanstus]

When passing MessageId as Header in MimeMessage constructor property is not initialized correctly.

For example:
var message = new MimeMessage(new Header(HeaderId.MessageId, MimeUtils.GenerateMessageId("mydomain.com")));

But in created message MessageId domain is <MY-PC-NAME> instead of mydomain.com

MimeKit Version: 3.1.0