Hello,

Environment

• isync/mbsync as my IMAP client
• proton-bridge from the protonmail-bridge-core on ArchLinux as as local bridge.
• Its backend IMAP library is, as you know today, Gluon.

Issue

When my .mbsyncrc contains an Expunge Both or an Expunge Far directive, I get the following error messages:

1. From mbsync:

IMAP command 'CLOSE' returned an error: operation not allowed

2. From protonmail-bridge:

Command failed cmd=CLOSE error="operation not allowed" pkg=gluon/session

This directive is defined as followed in the manual:

Permanently remove all messages [on the far/near side] which are marked for deletion.

Consequences

When disabling this directive (setting it to None), the error is gone, but locally deleted messages do not propagate on ProtonMail.
On the opposite, when settings this directive, the error is here, but deletion propagation (from local mail store (maildir) to remote mail store (protonmail) is working on my tests.

Thoughts

I'm not sure if I should have reported this problem to proton-bridge instead of here. Or if isync could be the problem (but since it is long-time project and work flawlessly for a number of people, I assumed the problem may be on the side on Gluon).