SMTP Error (550): Failed to add recipient, Been working fine for weeks, can no one solve this?

Maintenance
1

Just suddenly stopped sending, receiving ok.

Setup MIAB about a month ago, been working flawlessly. Everything is green in the /admin/status.
Lots of weird stuff in /var/log/mail.log that I don’t understand.

I can only send an email to myself. All others are rejected sending via Mac, iPhone or RoundCube.

Tried sudo mailinabox, then reboot. No change.

Below is the error from RoundCube:
SMTP Error (550): Failed to add recipient "my.name@halliburton.com" (5.1.1 my.name@halliburton.com: Recipient address rejected: halliburton.com).

2

Is that domain on any blacklists?

3

No Sir, my domain is not blacklisted as per MX Tool box.

4

Fair - can you look through postfix’s logs and see if any errors? (/var/log/mail I believe…?)

5

Here is the log when I send to any email other than my own domain.

Nov 10 17:30:03 box postfix/submission/smtpd[31205]: connect from unknown[204.98.7.11] Nov 10 17:30:04 box postfix/submission/smtpd[31205]: NOQUEUE: reject: RCPT from unknown[204.98.7.11]: 550 5.1.1 <luke.wu@OTHERDOMAIN.com>: Recipient address rejected: OTHERDOMAIN.com; from=<paddy@MYDOMAIN.com> to=<luke.wu@OTHERDOMAIN.com> proto=ESMTP helo=<[192.168.1.94]> Nov 10 17:30:04 box postfix/submission/smtpd[31205]: NOQUEUE: reject: RCPT from unknown[204.98.7.11]: 550 5.1.1 <john@OTHERDOMAIN.com>: Recipient address rejected: OTHERDOMAIN.com; from=<paddy@MYDOMAIN.com> to=<john@OTHERDOMAIN.com> proto=ESMTP helo=<[192.168.1.94]> Nov 10 17:30:04 box postfix/submission/smtpd[31205]: disconnect from unknown[204.98.7.11] Nov 10 17:30:18 imap-login: Info: Login: user=<paddy@MYDOMAIN.com>, method=PLAIN, rip=204.98.7.11, lip=107.170.195.36, mpid=31603, TLS, session=<6k9PJKpdagDMYgcL> Nov 10 17:30:18 imap(paddy@MYDOMAIN.com): Info: Disconnected: Logged out in=34 out=454

7

Is this a new install? Was the server able to send email before?

8

Was working flawlessly for about a month.
It seems Postfix is having trouble removing domain names.

I’m almost at the point of wiping and doing a fresh install when a find the time but I would really like to know whats going on and how to fix just incase it happens again.

9

Did a fresh install to fix in on a fresh droplet, new IP, the works.