IMAP server does not store outgoing emails - How can I change this?

Dear community,

I have integrated my Office365 mailbox into Zammad and noticed that sent items sent via Zammad are being stored on the Exchange server. Unfortunately, an IMAP server based on ESMTP Postfix running on Debian does not store outgoing emails. Is there a way to change this setting on the server so that outgoing emails are also saved just like incoming emails?

Thank you in advance for your help!

Postfix is a MTA, afaik it never stores mails in default configuration. Storing mails is part of a MDA, MUA or mail client. You can write a bcc rule, where postfix copies all sent mails to an internal mailbox.