Finally I got an email configuration that works for me, e.g. :

Real push based on IMAP idle
Lightweight - (low power/memory/CPU consumption).
Folders, spell checker, multiple accounts, IMAP, reliability, stability, configurability.
And (unlike modest) sends and receives email reliably (Modest never tells you when it fails)

Here is how it works, in 3-4 easy steps.
In Maemo
Install easy debian.

In easy debian
Install gnubiff and sylpheed.
Configure sylpheed to never check for new emails.
Configure gnubiff to monitor your email (via imap idle) and run sylpheed --receive.

In Maemo, as root.

add a script to /etc/network/if-up.d
"
sudo - u user debbie killall gnubiff
sudo -u user debbie gnubiff -n&
"
Chmod +x script.

add the following line to /etc/sudoers
root ALL=(ALL) ALL

Good luck, it's not as complicated as it looks and works great.
I don't think packaging on top of both easy debian and maemo is worth the effort.

(Thanks Qole, easy debian is what makes this phone worth it).