Login to Server

First, you can check the mail queue with this command

exim -bp

Next, copy the email ID from affected account and use this command to view the header

Example:

exim -Mvh 1jdIeW-00022q-P3

Next, to view the mail delivery logs and authentication use this command

cat /var/log/exim/mainlog | grep 185.29.11.12 | more

Then you can see email account authenticated and send the emails without any login failure

Login failure example:

2020-05-25 07:06:43 login authenticator failed for (User) [45.142.195.9]: 535 Incorrect authentication data (set_id=drm@com.my)

If login incorrect more than 15 times, the IP will auto blocked by directadmin