Solved SMTP Failure - AuthenticationInvalidCredentials: 5.7.0 Denied

[redeemtech]

Getting the error AuthenticationInvalidCredentials: 5.7.0 Denied during SMTP test. I've already read through the other thread and this isn't an issue with the static IP configuration. I've verified both internal and external DNS records for my 3CX domain and they both resolve to the same hostname, locally to my 192 address and externally to the static IP that's configured on the PBX.

During initial configuration, I did put the wrong 'local fqdn' in, but 3CX ended up registering the correct way. To try fixing this, I released the 3CX fqdn, and reinstalled 3CX and it went smooth, but the SMTP problem still isn't resolved. I'm not sure what to do at this point since SMTP is handled by 3CX. I believe this to be an internal error.

 

[cobaltit]

Never had any issues with 3CX SMTP and we handle a lot of installs. I'd try flipping your 3CX instance to dynamic and restarting the services (or reboot the instance) and then run the test. Let it sit that way for a bit and then set it back to static and test.

Also, it's not about resolution, it's about the outbound traffic. Your outbound traffic needs to come from the IP address defined in 3CX otherwise this is a no-go. Typically this happens when you have a router with mutiple WAN IPs and you aren't using the primary/default for 3CX. Routers will let you map inbound traffic for one of the aliased IPs to 3CX but your outbound traffic would go out as the primary IP. You'd need to to map your outbound traffic to that same IP in that case. I think your issue is just 3CX sorting out the FQDN bit though so setting it to dynamic for a bit should help it get sorted. And of course ensuring you are on v15.5 Update 6 or v16.

 

[redeemtech]

The first response and it's spot-on! The issue was outbound traffic. I had the 1:1 NAT in place, but it was after the PAT rule. Fixed that, and the issue is gone! I really appreciate the solid advice and I hope to return the favor to the community as I start deploying these systems.

 

[cobaltit]

Glad to hear it. That's the only time I've run into that issue and it was because we only handled the PBX and I couldn't get their IT folks to adjust the firewall.