I have an Ubuntu 16.04 server with ISPConfig Version: 3.1dev. and many websites installed. I know I have to update my system, but for some reason the email server is taking to much time to send the emails. I have to wait at least one hour for the emails to be sent when using the webmail (Roundcube od Squirrelmail), Outlook or my Gmail account. However, I installed WHMCS where I send emails automatically everyday at 10 am, and they are still sent instantly. I checked the email queue on ISPConfig but I didn't see any emails. Besides I checked postqueue -p but I didn't find anything neither
The file is /var/log/mail.log (or older versions with the same name and numeric extensions), you can use grep to search it ("grep [email protected] /var/log/mail.log" and such) or tail -f to watch it live, or use "less" or your favorite text editor to open and read through.