@deepanpd
Try this option also if option suggested by sunny not worked
Could not send email: [email protected]. The e-mail has been queued. Reason: Acquisition of thread lock expired, unable to notify [email protected] - IdentityIQ (IIQ) / IIQ Discussion and Questions - SailPoint Developer Community
One more
Mailjet protocol can used for sending out email from IIQ 8.4? - IdentityIQ (IIQ) / IIQ Discussion and Questions - SailPoint Developer Community