[Dovecot] How to manage email with an ISP restricted mailbox size?

[Tom Atkins]

Sorry if this is a bit off topic but I'm hoping list members here might
have some ideas.

Aim: use ISP provided email with restricted inbox size but keep an IMAP
accessible archive of emails (including 'sent' messages) on a remote server.

Scenario:

- Don't want to run my own SMTP server
- Have free ISP email with 1Gb mailbox limit and spam filtering that works
well
- Have remote server with plenty of disk space
- Want to use remote server for IMAP access to archive of email to avoid
1Gb ISP mailbox limit

Options I tried:

1. Use ISP email via IMAP and periodically backup / archive messages to
remote server with something like mbsync / isync to maildir format. Delete
old messages on ISP server safe in knowledge they are backed up on my
server. QUESTION: how to access those archives via IMAP (read only is OK)?

2. Use ISP email for sending messages only. Use Getmail / Fetchmail to move
messages to remote server and run Dovecot there. I tried using Getmail to
do this but couldn't figure out how to keep copies of 'Sent' and 'Draft'
messages if the email client was configured to read via IMAP on one server
and send via SMTP to another server.

Any thoughts on how best to achieve my aims?

Thanks, Tom.