==== 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): 0.9.5.1
- Linux/BSD distribution name and version: Ubuntu 16.04 x64
- 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:
====
Hi, I would like some help troubleshooting a recent issue. I've set up forwarding in some of the users' e-mail addresses from the main e-mail server (let's call it example.com) to their external accounts. E-mail between internal accounts at example.com work just fine, but users report that they're not getting any of the forwarded e-mails (while my own address has, at least to my Gmail account).

When checking /var/log/mail.log, I see this:

Jan 16 19:55:40 www postfix/smtp[14012]: 151FF80945: to=<user@externaldomain.com>, relay=externaldomain.com[EXTERNAL_IP]:25, delay=41, delays=0.01/0.02/21/20, dsn=5.0.0, status=bounced (host externaldomain.com[EXTERNAL_IP] said: 550-Verification failed for <internaluser@example.com> 550-Unrouteable address 550 Sender verify failed (in reply to RCPT TO command))

I can verify that internaluser@example.com exists. Reading about error 550 I see that it's related to a username spelled wrong or probable DNS errors, but I've run checks for DNS errors at mxtoolbox.com and they appear to be setup correctly. What would I need to do to fix this issue? Thanks in advance.