The Mailbox element has child elements named Sender and From. And I'm really confused about the difference between them.
This is what the documentation says about Sender:
The Sender element specifies the e-mail address of the person who sent an item
And about From:
The From element represents the address from which the message was sent
Really, it doesn't make any difference for me. The XML that I see is always the same for the both elements. So what is the real difference between these two?
In plain English:
From is who the message is from. It is who the recipient's email client should display the message is from.
Sender is usually the same as From, unless the message was originated by somebody, or some other system than the actual From address.
Example: Gmail when it's configured for a domain not hosted by Gmail. The From would contain you@yourdomain.com, but the Sender will contain someone@gmail.com. Many mail clients will render this as someone@gmail.com on behalf of you@yourdomain.com.
From Official RFC - Registration of Mail and MIME Header Fields
2.1.2. Header Field: From Description: Mailbox of message author [...] Related information: Specifies the author(s) of the message; that is, the mailbox(es) of the person(s) or system(s) responsible for the writing of the message. Defined as standard by RFC 822. 2.1.3. Header Field: Sender Description: Mailbox of message sender [...] Related information: Specifies the mailbox of the agent responsible for the actual transmission of the message. Defined as standard by RFC 822.