Security deposit return with no forwarding address

[Dana Holland]

Tenants moved out at the end of last month.  I need to return their security deposit by the 18th (per local landlord tenant laws).  I emailed them a week before move out to request a forwarding address and letting them know they could either leave the keys in a drawer in the kitchen, or drop them off at our realtor's office.  I never received an email response.  The last day of the lease they showed up at the realtor's office with all the keys.  They verbally asked her to have us leave the security deposit check with her for them to pick up later as they don't have a forwarding address (?!).  Local landlord tenant laws say that I have to mail the deposit via first class mail to the last known place of residence unless tenants make other arrangements in writing.  Should I email them again and ask them to confirm via email that they want the deposit dropped with the realtor?  Is an email considered a written request should this escalate to a court scenario?  Just want to make sure I am covered as I would owe them twice the amount of the deposit if it's not given back to them on time.

May or may not be worth mentioning that these people are manipulative and not trust worthy.  I'm somewhat skeptical that they are playing a game to try to get more back than they deserve.