==== Required information ====
- iRedMail version (check /etc/iredmail-release):
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
======== Required information ====
- iRedMail version (check /etc/iredmail-release):
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
====- iRedMail version (check /etc/iredmail-release): 0.9.0 (For some reason, 0.9.2 wasn't working and I decided to just install older version)
- 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
- Related log if you're reporting an issue: N/A?

Alright, so I have seen a similar question posted here and other places once or twice, but no proper answers.

Anyway, I have a couple of VPSs and a shared web server. One of my VPSs I use as an email server, using our goold old friend IRM! The shared host server (from TSOHost) has its own set up. Anyway, when I send an email from my shared server to IRM, or vice versa, I get an error "550 No Such User Found". Now I know my DNS settings are correct and working, but what's strange is it's only some servers. For instance, Gmail servers are fine and don't even put my IRM mail into spam folders, however the shared host server gives errors. These are the errors I receive:

When I send to my IRM server from shared host:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  j*****@chloecrayola.co.uk
    No Such User Here

And when I send from IRM to shared host:

This is the mail system at host ns2.chloecrayola.co.uk.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<t****@byonex.co.uk>: host byonex.co.uk[185.24.98.182] said: 550-Verification
    failed for <j****@chloecrayola.co.uk> 550-No Such User Here 550 Sender
    verify failed (in reply to RCPT TO command)

I'm not incompetent, but I'm not a Linux wizard (or rather email wizard, I'm better at other stuff), so I'm not too sure what this means. I'm assuming its some sort of thing disabled in postfix, or perhaps a messed up file. Either way, the problem is with all my IRM addresses, not just one.

Happy to post any other files if it helps <3