Seems like your SASL plugin most probably isn’t configured correctly. You should check your postfix main.cf and master.cf and make sure SASL authentication is properly set up.
@bomtack check your ports if you hosting from home/residential isp and apply common sense. Just have look at the config - its there with click of the mouse. Virtualmin provide excellent access to this problem.
I know I already said this but your problem is most probably caused by a postfix/sasl misconfiguration. You’ll have to manually go through your configuration files to further pinpoint the cause of the authentication failure (and fix it).
What OS and version are you using? I don’t think any supported OS should have Postfix running in a chroot, by default…so, I’m not sure how you got there. But, if it does happen automatically on some distro, I’d want to know about it (and maybe fix it).
CentOS 8 definitely does not setup Postfix to run in a chroot by default. So, it had to have been changed (by you or someone else). So…for the future, don’t do that, and you won’t have this problem.
Then it was changed in the image your host used, and it wasn’t a “fresh” install.
The other solution to this problem would be to switch all of your postfix processes back to not being in a chroot (in /etc/postfix/master.cf). chroot is often believed to be a security feature…but, it mostly isn’t, and it makes management more complicated/confusing especially for new users.