For postfix to work for this i need to have the full SMTP+IMAP configured
You are associating SMTP and IMAP. They are unrelated. Completely and totally unrelated.
Postfix is SMTP, it has no association with IMAP handling.
Just install Postfix and your sending is fixed. Just put in your IMAP details of your Gmail account and your IMAP is fixed because your application absolutely has a built in IMAP client, that's what those settings are for. Those settings cannot work unless it is a client.