Mail not sending from helpdesk

Mail not sending from helpdesk

Hi

We are using Service Desk Plus 9.1 with Data Base PGSQL
SMTP settings configured with Gmail. (configurations we tested using thunderbird client from the tool installed machine)

but mails are not sending out from the tool, while sending, mail sending failed message getting.

how to troubleshoot this issue.

Thanks
Anoop PS
Mob - 9995822232

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