One of the most common collections questions I get is “I loaned X some money, but didn’t make them sign anything. Can I sue them?” The simple answer is yes.
As long as the person making the promises is also the borrower, you’re safe. Issues arise, though, when you’re enforcing a promise by a third party to pay the debts of another. This is called a “Guaranty” (or, depending on how old a lawyer you are, a “Guarantee”).
However you spell it, a guaranty has to be in writing to be enforceable.
Under Tennessee’s version of the Statute of Frauds, no party may file a lawsuit “[t]o charge the defendant upon any special promise to answer for the debt, default, or miscarriage of another person…. unless the promise or agreement, upon which such action shall be brought, or some memorandum or note thereof, [is] in writing, and signed by the party to be charged therewith, or some other person lawfully authorized by such part ” See Tenn. Code Ann. § 29-2-101(a)(2).
So, then the question becomes, how formal does a writing have to be? Can it be hand-written? Can it be an email?
Guaranty agreements are strictly construed and, in order find a guaranty, the language must contain the clear and unambiguous intent that the guarantor is agreeing to be liable. For more on guaranties (or guarantees), be sure to check out the Tennessee Supreme Court in 84 Lumber Co. v. Smith, 356 S.W.3d 380, 384 (Tenn. 2011).
In the case of an email, I’d ask “Is the email’s language clear and unambiguous in stating that Y is willing to pay the debts of X?” If so, I think it satisfies the Statute of Frauds.
Creditors Rights 101 
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