Hi @parth_agrawal,
have you checked this: V11 can't suspend nor resume email queue - #6 by Himanshu_Mishra
If all fails, this is a bulletproof workaround 
V11 can't suspend nor resume email queue - #10 by lasalesi
Hi @parth_agrawal,
have you checked this: V11 can't suspend nor resume email queue - #6 by Himanshu_Mishra
If all fails, this is a bulletproof workaround V11 can't suspend nor resume email queue - #10 by lasalesi