The Millwall goalkeeper, 34, said via his Twitter account that he would be moving to North Lincolnshire on loan from the Championship side Millwall.
"Thank you very much 4 the warm welcome. Looking 4ward to meeting everyone Monday," he wrote.
Mildenhall will bring a great deal of experience to the Iron's back line, having played in 377 first-team games since first coming through the ranks at Swindon Town in 1995.
He is likely to go straight into the Iron's squad to face Walsall on Tuesday night, displacing current keeper Sam Slocombe.