I'll assume that they didn't send this certified. Here's the actual law:
83.49 Deposit money or advance rent; duty of landlord and tenant.—
(3) The landlord or the landlord’s agent may disburse advance rents from the deposit account to the landlord’s benefit when the advance rental period commences and without notice to the tenant. For all other deposits:
(a) Upon the vacating of the premises for termination of the lease, if the landlord does not intend to impose a claim on the security deposit, the landlord shall have 15 days to return the security deposit together with interest if otherwise required, or the landlord shall have 30 days to give the tenant written notice by certified mail to the tenant’s last known mailing address of his or her intention to impose a claim on the deposit and the reason for imposing the claim. The notice shall contain a statement in substantially the following form:
This is a notice of my intention to impose a claim for damages in the amount of upon your security deposit, due to . It is sent to you as required by s. 83.49(3), Florida Statutes. You are hereby notified that you must object in writing to this deduction from your security deposit within 15 days from the time you receive this notice or I will be authorized to deduct my claim from your security deposit. Your objection must be sent to (landlord’s address) .
If the landlord fails to give the required notice within the 30-day period, he or she forfeits the right to impose a claim upon the security deposit and may not seek a setoff against the deposit but may file an action for damages after return of the deposit.
Notice that it specifically says "certified mail". It's clear that he knew your address, because he sent the check to it. So the fact that he sent the message via email indicating his intention to deduct is not enough. The law specifically says certified, and says that if it's not complied with, he waives his rights. It's also upon vacating. But if I were you, I would wait until October 1 or 2, then say that this wasn't certified, so under this law he has to return everything to you.
Send a demand letter demanding payment within 30 days, otherwise you will pursue legal action against him, seeking that amount plus any additional damages as allowed by law. Send this letter certified, return receipt requested, as well as a copy sent regular mail. Keep a copy for yourself, as well as the return receipt number so that you can show the court that you made a demand for the unpaid security deposit
If he still doesn't pay, Do a search on the web for your county and "small claims court." You should find either a website or phone number to the small claims clerk. Ask them what you need to do to bring such a lawsuit. The small claims clerk will give you guidance on how to file this suit and how to get the other party served with notice. You will receive a hearing date, at which you should present your evidence and ask for a judgment for the amount that you should be paid..
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable.
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Thank you, ***** ***** luck to you!