MAGNOLIA-2451 introduced mimeMultipart property into MailAttachment. The property specifies in which part of structure of MgnlMultipartEmail will be attachment added. The mimeMultipart property should have values "mixed" or "related", with different value will be treated as "mixed". And for backward compatibility with mail templatesConfiguration. MailAttachments with not specified (null value) mimeMultipart property will be treated as "related".

Property mimeMultipart values:

• mixed - attachment will be added like normal attachments to the email
• related - the attachment which are shown in text part of message

Also MailAttachment doesn't use cid property anymore (don't know why or when this was removed). For Content-ID is used attachment name (not file name).