I noticed this several times and wondering if there is a reason for Carbon Copying themselves on a email when sent to others?
closed as primarily opinion-based by LPChip, Ramhound, DavidPostill♦ Jun 1 '17 at 12:50
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The accepted answer
Most people I know that exhibit this behavior is so they have an email in their inbox that continues the chain, and they can see their response in the timeline continuity of the chain. If you don't CC yourself, most email clients do not show your response, as it goes to the "Sent" folder, and does not appear in your Inbox or the same folder the email chain is in.
I set up rules in Outlook where if an email contains "Project A" in the subject, it should be routed to the "Project A" folder in my inbox. When I CC myself in these emails, I can be sure that my "Project A" folder contains all related emails, including those that I sent.
It also means that I can periodically clear out my Sent Mails folder without worrying about losing project specific emails.
I find this is one example of good workaround of email system
Typically, it's because they're accessing their email through a POP3 server which means that sent emails are only stored locally (unlike IMAP). They would do this regularly if they happened to use more than one client as it would allow them to see the sent email from all clients (as it's stored in the Inbox, which is accessible to all clients when using POP3).
This is a reason, amongst others, to use IMAP rather than POP so as to avoid this rigmarole.
Just like @David Morris answer, as a support to non-tech savvy users, they only want to view the message they've sent in one folder (Inbox) rather than searching the Sent folder.
Though I find this as a sign of being disorganized, as long as it works for them, I won't complain.
Obviously there are a large number of possible reasons, but one reason that I know of is to store messages in a folder that's not the sent folder. They may have rules set up that automatically put emails in different folders within Outlook, and they want to capture their responses in those same emails.
They may also be sending it to an additional email address so that they can chronicle it there. For example, I use a different email account for job searching than I do for personal use, I always BCC the personal email account when I'm using the job searching account so I can find my messages if I need to.