Hi,
I think you should following these steps I am sure they will worked properly and also important to access:
Check Documentation and Changelog: Look at the latest Dovecot documentation and changelogs to see if there are any notes about the imap_zlib plugin being moved renamed or deprecated.
Rebuild with Plugin: Ensure you have the necessary dependencies installed for zlib and then rebuild Dovecot with plugin support by configuring it explicitly. You can use the configure with zlib option before compiling.
Check for Alternative Repositories: Sometimes plugins may be maintained separately. Check if there is an independent repository or branch that includes the imap zlib plugin.
Contact Dovecot Community: If the plugin has been removed, consider reaching out to the Dovecot community or mailing list for alternative solutions or to understand the reason for its removal.
Thanks