I'm using it for 1-on-1 chats in my family and the application makes you forget that it's smtp/imap/pgp underneath. It feels like a WA clone. Will it disclose past message contents on private key leak? yes.
If you fetch mails via pop3 be aware, you'll move them away before DeltaChat can move them into its own folder via IMAP to build its message threads. If you're doing IMAP only you'll see the messages with your mailclient unless moved. Maybe consider using a dedicated email-alias or account. If the receiving SMTP on submission doesn't strip your connecting IP Address in the Received headers this is quiet a lot on the wire that DC can't do anything about and where you would rely on transport encryption.
It made a point what a thoughtful chat-view, pgp-using email client can do, so I still recommend to give it a try.
I have only tested gmail to gmail and it was fairly quick. Under a second in my experience. Providers will differ but email is usually very fast these days.
If you fetch mails via pop3 be aware, you'll move them away before DeltaChat can move them into its own folder via IMAP to build its message threads. If you're doing IMAP only you'll see the messages with your mailclient unless moved. Maybe consider using a dedicated email-alias or account. If the receiving SMTP on submission doesn't strip your connecting IP Address in the Received headers this is quiet a lot on the wire that DC can't do anything about and where you would rely on transport encryption.
It made a point what a thoughtful chat-view, pgp-using email client can do, so I still recommend to give it a try.