@nikolal You mean on the server?
@nikolal @hyde_stevenson This is purely server-side feature. SMTP normally doesn't care about folders on the server-side, folders are IMAP thing.
Seems like Gmail's SMTP does that as a courtesy feature, while Disroot just does what SMTP is supposed to.
Thunderbird for example will first send a message using SMTP (for actual delivery), and then use IMAP to store a copy of the same message in Sent folder.