1. Who can manage the maillist? He must be the one belong to his domain, but only can add existed user to his maillist or remove in-list-user from maillist. No add new or delete mail-user in the mail domain.

Short answer: Admins assigned to this domain can manage mail list.

Domain admin is not required to be a member of this domain, because it's not a mail user.

You can implement this with postfix RESTRICTION CLASS in hash db format. But iRedAdmin can't/won't modify files on file system directly, so it's impossible to implement this feature in iRedAdmin.

If you don't want to use hash db format, you can try other mail list access policy daemon.

Not implemented in v1.0 yet, but we will implement this in future release.
With this feature support, you have to upgrade iRedMail to at least 0.5.1.

I focus on your admin panel (full-featured).

There are some functions missed

1. Who can manage the maillist? He must be the one belong to his domain, but only can add existed user to his maillist or remove in-list-user from maillist. No add new or delete mail-user in the mail domain.

2. Who can can email to the maillist? Beside the users in maillist, can the maillist-admin allow his group receive email from other account (this account is not in his maillist) or all others account or deny from all others account?

3. Can maillist-admin add external email to his maillist?

These functions are very important to a maillist.