I turn to you asking developers think about a few useful fixes. Following are the points that would make me interested as I'm sure other members of the panel as well.
1. The DNS TXT record with the possibility to give a name (Example: _dmarc.example.com. IN TXT "v = DMARC1; p = none" not example.com. IN TXT "v = DMARC1; p = none")
Mainly it comes to give a name to a TXT record, not just the domain.
2. PTR DNS record type might stupid but for example I would like to be able to add the zone / domain in in-addr.arpa possibly ip6.arpa.
3. Appendix OpenDKIM you can add or remove individual customer's domain and not, as now all or nothing. It would be good to make the customer also had the power to DKIM key installation for your domain, for example, if the administrator allow for such an operation by an additional variable when setting up a customer account.
4. SSL Certificates may have to have an option on / off. Some sellers do not want to give most of the options for a low price package.
5. The problem with the capacity of e mail accounts (tested on i-MSCP 1.2.9) if the seller changes the allocation of capacity email accounts is all a customer's account gets equally. Example: 10 e-mail accounts after changing the limit a client's account by the reseller to 1GB. This splits the 1GB for 10 pieces of the 100MB and each account change the existing capacity of the 100MB each. Automation probably not quite working as it should do unless there is a switch in the panel settings to avoid such a situation.