What is the importance of Content ID in mail? Is there any difference in the way this value is set across the most popular mail clients say Thunderbird, Microsoft Outlook and so...
What are things a developer should have in mind while providing a service that is related to reading mails sent from different clients to provide cross client compatibility, specifically with Content ID?
Thanks and Regards,
The first thing to keep in mind is that the Content-ID header for a body part is optional. It's mostly only needed for multipart/related parts.
You should read RFC 2045, which defines the Content-ID header.
What were you planning to use the Content ID for?