MailWizz - Email Marketing Application 2.6.6

[ADD] - Beside "Campaigns abuse complaints" in customer area, we have added "Campaigns abuse reports" too
[ADD] - Added setting to decide whether the customer gets notified via email on abuse complaints or not
[ENH] - The "From" address used in delivery servers will now be unique across customers. No two customers can use same "From" address
[RMV] - Remove the X-Receiver and X-Sender headers which we added by default
[MSC] - Overall fixes
[UPD] - Updated composer packages

[ENH] - Campaign reschedule now uses mutexes and a control flag to prevent creating multiple campaigns instead of just one
[ADD] - Added ability for important transactional emails to fallback on system servers
[ADD] - Added ability to parse campaign custom tags inside the random content blocks

[BUG] - Fix the parsers for campaign xml/rss and json feeds for PHP 8
[BUG] - Make sure tags inside XML feeds are parsed as late as possible to avoid issues like creating separate tracking links for each parsed tag
[MSC] - Overall fixes
[UPD] - Updated composer packages