diff --git a/build.gradle.kts b/build.gradle.kts
index 80d7ccd..d7fcc6d 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -28,12 +28,14 @@ repositories {
 
 dependencies {
     val mysqlConnectorJ = "9.5.0"
+    val commonsValidator = "1.10.1"
     implementation("org.springframework.boot:spring-boot-starter-actuator")
     implementation("org.springframework.boot:spring-boot-starter-web")
     implementation("org.springframework.boot:spring-boot-starter-data-jpa")
     implementation("com.mysql:mysql-connector-j:${mysqlConnectorJ}")
     implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
     implementation("org.jetbrains.kotlin:kotlin-reflect")
+    implementation("commons-validator:commons-validator:${commonsValidator}")
     developmentOnly("org.springframework.boot:spring-boot-devtools")
     annotationProcessor("org.springframework.boot:spring-boot-configuration-processor")
     testImplementation("org.springframework.boot:spring-boot-starter-actuator-test")
diff --git a/src/main/kotlin/net/halfbinary/scavengerhuntapi/controller/SignupController.kt b/src/main/kotlin/net/halfbinary/scavengerhuntapi/controller/SignupController.kt
index 7929f49..496d62e 100644
--- a/src/main/kotlin/net/halfbinary/scavengerhuntapi/controller/SignupController.kt
+++ b/src/main/kotlin/net/halfbinary/scavengerhuntapi/controller/SignupController.kt
@@ -3,6 +3,7 @@ package net.halfbinary.scavengerhuntapi.controller
 import net.halfbinary.scavengerhuntapi.model.converter.toDomain
 import net.halfbinary.scavengerhuntapi.model.request.HunterSignupRequest
 import net.halfbinary.scavengerhuntapi.service.SignupService
+import org.springframework.http.ResponseEntity
 import org.springframework.web.bind.annotation.PostMapping
 import org.springframework.web.bind.annotation.RequestBody
 import org.springframework.web.bind.annotation.RestController
@@ -10,7 +11,13 @@ import org.springframework.web.bind.annotation.RestController
 @RestController
 class SignupController(private val signupService: SignupService) {
     @PostMapping("/signup")
-    fun hunterSignup(@RequestBody body: HunterSignupRequest) {
-        signupService.createNewHunter(body.toDomain())
+    fun hunterSignup(@RequestBody body: HunterSignupRequest): ResponseEntity<Any> {
+        try {
+            signupService.createNewHunter(body.toDomain())
+            return ResponseEntity.ok().build()
+        } catch (e: RuntimeException) {
+            return ResponseEntity.badRequest().body(e.message)
+        }
+
     }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/net/halfbinary/scavengerhuntapi/error/exception/InvalidEmailException.kt b/src/main/kotlin/net/halfbinary/scavengerhuntapi/error/exception/InvalidEmailException.kt
new file mode 100644
index 0000000..51206cc
--- /dev/null
+++ b/src/main/kotlin/net/halfbinary/scavengerhuntapi/error/exception/InvalidEmailException.kt
@@ -0,0 +1,3 @@
+package net.halfbinary.scavengerhuntapi.error.exception
+
+class InvalidEmailException(email: String): RuntimeException("The email ${email} is not valid.")
\ No newline at end of file
diff --git a/src/main/kotlin/net/halfbinary/scavengerhuntapi/error/exception/PreexistingAccountException.kt b/src/main/kotlin/net/halfbinary/scavengerhuntapi/error/exception/PreexistingAccountException.kt
new file mode 100644
index 0000000..7b8526a
--- /dev/null
+++ b/src/main/kotlin/net/halfbinary/scavengerhuntapi/error/exception/PreexistingAccountException.kt
@@ -0,0 +1,3 @@
+package net.halfbinary.scavengerhuntapi.error.exception
+
+class PreexistingAccountException: RuntimeException("An account with that email already exists.")
\ No newline at end of file
diff --git a/src/main/kotlin/net/halfbinary/scavengerhuntapi/repository/HunterRepository.kt b/src/main/kotlin/net/halfbinary/scavengerhuntapi/repository/HunterRepository.kt
index 56b8ac5..254cf4b 100644
--- a/src/main/kotlin/net/halfbinary/scavengerhuntapi/repository/HunterRepository.kt
+++ b/src/main/kotlin/net/halfbinary/scavengerhuntapi/repository/HunterRepository.kt
@@ -6,4 +6,7 @@ import org.springframework.data.jpa.repository.JpaRepository
 import org.springframework.stereotype.Repository
 
 @Repository
-interface HunterRepository : JpaRepository<HunterRecord, HunterId>
\ No newline at end of file
+interface HunterRepository : JpaRepository<HunterRecord, HunterId>
+interface HunterRepository : JpaRepository<HunterRecord, HunterId> {
+    fun findByEmail(email: String): HunterRecord?
+}
\ No newline at end of file
diff --git a/src/main/kotlin/net/halfbinary/scavengerhuntapi/service/SignupService.kt b/src/main/kotlin/net/halfbinary/scavengerhuntapi/service/SignupService.kt
index 42e608b..068f431 100644
--- a/src/main/kotlin/net/halfbinary/scavengerhuntapi/service/SignupService.kt
+++ b/src/main/kotlin/net/halfbinary/scavengerhuntapi/service/SignupService.kt
@@ -1,13 +1,22 @@
 package net.halfbinary.scavengerhuntapi.service
 
+import net.halfbinary.scavengerhuntapi.error.exception.InvalidEmailException
+import net.halfbinary.scavengerhuntapi.error.exception.PreexistingAccountException
 import net.halfbinary.scavengerhuntapi.model.converter.toRecord
 import net.halfbinary.scavengerhuntapi.model.domain.Hunter
 import net.halfbinary.scavengerhuntapi.repository.HunterRepository
+import org.apache.commons.validator.routines.EmailValidator
 import org.springframework.stereotype.Service
 
 @Service
 class SignupService(private val hunterRepository: HunterRepository) {
     fun createNewHunter(hunter: Hunter) {
+        if (!EmailValidator.getInstance().isValid(hunter.email)) {
+            throw InvalidEmailException(hunter.email)
+        }
+        if (hunterRepository.findByEmail(hunter.email) != null) {
+            throw PreexistingAccountException()
+        }
         hunterRepository.save(hunter.toRecord())
     }
 }
\ No newline at end of file