How do emails get in the "sent" folder?

Question

I feel dumb for asking this since i've been sending and receiving emails in my code for some time. But...

Who is moving emails to the "sent" folder after sending? Is it the client or the server?

Answer 1

Usually this is done by the mail client.

This is both more efficient hen sending a mail to the SMTP server and having that send a copy back to you to put in the 'sent' folder. It also needs no extra logic on the mail clients side to recognize a 'oh, a just send this and now I am getting it back. Maybe I should move it to the send folder'.

Note that depending on the mail client mail in the send folder might not actually have been send. E.g. in outlook it just means that the client tried to send it (if it failed it will still store a copy in the send folder).