Also, "in:" in a misnomer as emails aren't "in" a mailbox, GMail uses tags / labels. So technically you can label an email as both sent and inbox (include yours

Also, "in:" in a misnomer as emails aren't "in" a mailbox, GMail uses tags / labels. So technically you can label an email as both sent and inbox (include yourself in the recipient list). This label rather than mailbox approach is clearly visible if you ever use the IMAP interface to GMail; it breaks assumptions / guidelines / rules in the IMAP protocol. On top of that GMail sometimes treats some special labels as exclusive to other special labels (i.e. some of the built in always available labels). i.e. something can't have the inbox and trash labels at the same time.