fix: Check if email account exists before picking signature
fix: Check if email account exists before picking signature

(cherry picked from commit 2e5bd71d95c1ab2d5d089945da6065b1a059ae59)

StrellaGroup/frappe,frappe/frappe,yashodhank/frappe,frappe/frappe,yashodhank/frappe,yashodhank/frappe,StrellaGroup/frappe,StrellaGroup/frappe,yashodhank/frappe,frappe/frappe