DUPLICATE CASES once we changed mail server settings to Modern authentication

DUPLICATE CASES once we changed mail server settings to Modern authentication

Dear,
please note, that from the moment when we switch the mail server settings to Modern one few months ago.

ServiceDesk starts acting strange and is creating duplicate tickets, so informing requestor several times but with different CASE number. Also we see, that INBOX once the ticket is creating keeps emails instead of deleting them.

Any suggestion what can be changed?

Later I will share the unprofessional support ticket handled by low level technician for more then few months, without even small improvement. Very frustrating. 

Thanks
Roman