Saturday, 19 Mar, 2016 exim The following is just some random advice derived from my experience on dealing with email-related issues. More specifically, here I'll be referring to exim (a very popular mail daemon), Cpanel/WHM & CentOS. Check if the user & password combination is correct. Check if the SMTP Authentication is enabled. Check if the User's mailbox is full. Perform an nslookup of the domain thru a public DNS Server. Perform an nslookup of the MX RRs thru a public DNS Server. Verify that the SPF RR is applied to the domain. Telnet (or putty with the telnet option enabled) to the destination server address to see if it answers. Check if the domain name is present inside /etc/localdomains. Check the logs with exigrep /var/log/exim_mainlog. Check with vi /etc/userdomains Look for some blank spaces or broken lines near the domain that is having incorrect authentication data issue error 535 Check whether the folder "etc" within /home/"cpanel-username"/etc/ is owned by cpanel-username:mail If it is not then change it with: chown username:mail /home/username/etc/ -R Hope you might find those useful & feel free to share your own special/unique checks on the comments section. Rate this post Andrea MatesiSenior Professional Network and Computer Systems Engineer during work hours and father when home. Andrea strives to deliver outstanding customer service and heaps of love towards his family. In this Ad-sponsored space, Andrea shares his quest for "ultimate" IT knowledge, meticulously brought to you in an easy to read format. Share this:LinkedIn Related