@Sandeep Saxena - headers are set in /apps/console/commands/SendCampaignsCommand.php at line ~ 1253. You might comment line what you don't want.
@miojamo - try this:
/usr/local/bin/php -q /home/send/public_html/apps/console/console.php send-transactional-emails --verbose=1
@tizaj - check this - https://forum.mailwizz.com/threads/gmail-spam-yahoo-is-fine.5608/#post-36249
@Yas King - you can upload some screenshots with this issue?
@tizaj - check this - https://forum.mailwizz.com/threads/general-error-2006-mysql-server-has-gone-away.3853/#post-24960
@GregKevey - check this - https://forum.mailwizz.com/threads/bounce-with-amazon-ses-not-working.4762/#post-31860
@nemesis82 - Check this article https://kb.mailwizz.com/articles/my-campaigns-dont-send-theyre-stuck-in-pending-sending-status/
@kavin - were you have change font?
@Lazaros - This is not possible.
@michael chu - you can attach a screenshot ?
@Mils - Check this -> https://kb.mailwizz.com/articles/debug-send-campaigns-command/
@Alex Read - check this https://api-docs.mailwizz.com/
@Anri Hakobyan - You tried to reinstall?
@tatsujin90 - Check if you have some issues in backend - misc - application log, or you can upload a screenshoot with logs.
@ltdviso - Check number 8 from this article https://kb.mailwizz.com/articles/performance-improvements/
Separate names with a comma.