Case 1 (Less)

Cause: DNS issue

Solution: Check /etc/resolv.conf for correct record. You can use the nameserver below:

nameserver 8.8.8.8
nameserver 8.8.4.4

Case 2 (Common)

Cause: An email account spamming and causing the email counter to reach limit. /etc/virtual/usage/<<user>>

Solution:
1) Check /var/log/exim/mainlog for spammer
2) Change that email account password
3) Reset counter. Replace <<user>> with directadmin username.

echo "X" > /etc/virtual/usage/<<user>>

Note echo "X" is referring to the number of emails send limit set for that particular <<user>>

Example: echo 200 > /etc/virtual/usage/<<user>>

Reference:
https://help.directadmin.com/item.php?id=455
https://help.directadmin.com/item.php?id=81

Updated on: 18 / 12 / 2018