==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.7 MARIADB edition.
- Linux/BSD distribution name and version: Centos 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Apache
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

I am unable to receive email from a specific host

This is a log on my mail server for what's happening at the time the email is being received from the remote host.

The only thing that I'm getting out of this is that there was a protocol issue, but I can receive email from other hosts, and the remote host can send email to other hosts.

I have been unable to find more information about a 550 5.5.1 that might make sense in this situation. Any help would be greatly appreciated.

Apr 19 22:58:35 mail postfix/postscreen[3428]: CONNECT from [x.x.x.x]:65308 to [a.a.a.a]:25
Apr 19 22:58:35 mail postfix/postscreen[3428]: PREGREET 32 after 0.1 from [x.x.x.x]:65308: HELO mailserver.example.com\r\n
Apr 19 22:58:40 mail postfix/postscreen[3428]: NOQUEUE: reject: RCPT from [x.x.x.x]:65308: 550 5.5.1 Protocol error; from=<origin.source@origin.example.com>, to=<local.destination@local.example.com>, proto=SMTP, helo=<mailserver.example.com>
Apr 19 22:58:56 mail postfix/postscreen[3428]: HANGUP after 16 from [x.x.x.x]:65308 in tests after SMTP handshake
Apr 19 22:58:56 mail postfix/postscreen[3428]: DISCONNECT [x.x.x.x]:65308

Additionally origin.example.com and mailserver.example.com are the remote server, whereas local.example.com is my server and should be considered entirely different domains.