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My team has been communicating with an outside party that uses Office365 encryption. When they send an email to my team, the message I see looks like this:

To: teammemberA@mycompany.com, teammemberB@mycompany.com, me@mycompany.com

Body: You've received a protected email from outside party ... sign in using the following email address: me@mycompany.com

However, Team Member A sees the body as telling them to sign in using "teammemberA@mycompany.com", not "me@mycompany.com".

I was just wondering how Office365 manages this? Is there a feature of HTML email, or an Exchange server trick that lets you specify that a recipient should see their own email address? My company uses Outlook as the email client, and Exchange as our email server, so is this an Outlook- or Exchange-specific feature I don't know about?

Sam Skuce
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Emails have a concept of an envelope, and it works just like a paper envelope. If you send a paper letter (email) to multiple people, you put everyone's name at the top of the letter (email) but you only put one name on each envelope (envelope). If you were to put multiple names on the envelope, how would the post office (mail server) know which person to deliver that copy to?

When an email server connects to the recipient's mail server, it starts off by saying "email from x for y" (envelope), then it sends the actual message (email).

Like a paper letter, just because the email says it was sent to multiple people, doesn't mean it actually was. And just because the email says it was sent to multiple people, doesn't mean they all received the same content.

longneck
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  • Ah, I didn't realize that you could put an entirely inaccurate "To" field in the message body when transferring over SMTP. I just hand-typed a test to prove it. I had always assumed that the "To" field was copied directly from the "RCPT TO" fields in the SMTP data exchange. I guess that makes sense, because you wouldn't send "RCPT TO" commands for people in, e.g. another domain, but you do want the recipient to know those addresses as well. Obviously, I don't write mail servers for a living =). I'll hold off on giving you the checkmark for 24 hours, as is tradition, but this is it. Thanks! – Sam Skuce Sep 13 '19 at 20:15
  • Such good explanation given by longneck. It seems the issue has been resolved. You can mark it as the best answer. – Beverly Gao Sep 16 '19 at 05:31