Essex Head Coach Paul Grayson said he was delighted Mahmood had joined the club.
"I like cricketers who feel they have point to prove to people and he has lots of ability, he's experienced and he's a fit guy who can bowl with good pace as well so we feel Saj will be a real addition to the squad."
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Sunny spells and isolated showers expected through the day.
After months of scout-like preparation, the Essex International Jamboree is underway in a field near Chelmsford
Mostly dry overnight. Sunny spells and isolated showers on Sunday.