diff --git a/build.gradle b/build.gradle
index 7b51184..9bf22d4 100644
--- a/build.gradle
+++ b/build.gradle
@@ -15,6 +15,7 @@ java {
 
 repositories {
 	mavenCentral()
+	maven { url 'https://jitpack.io' }
 }
 
 dependencies {
@@ -44,10 +45,9 @@ dependencies {
 	implementation 'io.awspring.cloud:spring-cloud-aws-s3:3.1.0'
 	implementation 'javax.xml.bind:jaxb-api:2.3.1'
 
-	// mail
-	implementation 'org.springframework.boot:spring-boot-starter-mail'
-	implementation 'org.springframework.boot:spring-boot-starter-thymeleaf' // option
-	implementation 'nz.net.ultraq.thymeleaf:thymeleaf-layout-dialect' // option
+	// brevo
+	implementation 'com.sendinblue:sib-api-v3-sdk:7.0.0'
+
 
 	// lombok
 	implementation 'org.projectlombok:lombok'
diff --git a/src/main/java/com/writon/admin/domain/controller/AuthController.java b/src/main/java/com/writon/admin/domain/controller/AuthController.java
index 90ccff6..e4deeca 100644
--- a/src/main/java/com/writon/admin/domain/controller/AuthController.java
+++ b/src/main/java/com/writon/admin/domain/controller/AuthController.java
@@ -1,16 +1,13 @@
 package com.writon.admin.domain.controller;
 
 import com.writon.admin.domain.dto.request.auth.LoginRequestDto;
-import com.writon.admin.domain.dto.request.auth.ReissueRequestDto;
 import com.writon.admin.domain.dto.request.auth.SignUpRequestDto;
 import com.writon.admin.domain.dto.response.auth.LoginResponseDto;
-import com.writon.admin.domain.dto.response.auth.ReissueResponseDto;
 import com.writon.admin.domain.dto.response.auth.SignUpResponseDto;
 import com.writon.admin.domain.dto.wrapper.auth.LoginResponseWrapper;
 import com.writon.admin.domain.service.AuthService;
 import com.writon.admin.global.config.auth.CookieProvider;
 import com.writon.admin.global.response.SuccessDto;
-import jakarta.servlet.http.HttpServletRequest;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.ResponseEntity;
diff --git a/src/main/java/com/writon/admin/domain/service/AuthService.java b/src/main/java/com/writon/admin/domain/service/AuthService.java
index 0082937..90f221c 100644
--- a/src/main/java/com/writon/admin/domain/service/AuthService.java
+++ b/src/main/java/com/writon/admin/domain/service/AuthService.java
@@ -27,7 +27,6 @@
 import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
-import org.springframework.security.core.userdetails.UsernameNotFoundException;
 import org.springframework.security.crypto.password.PasswordEncoder;
 import org.springframework.stereotype.Service;
 
diff --git a/src/main/java/com/writon/admin/domain/service/ChallengeService.java b/src/main/java/com/writon/admin/domain/service/ChallengeService.java
index 31643f0..7fc7315 100644
--- a/src/main/java/com/writon/admin/domain/service/ChallengeService.java
+++ b/src/main/java/com/writon/admin/domain/service/ChallengeService.java
@@ -30,13 +30,9 @@
 import com.writon.admin.global.error.ErrorCode;
 import java.time.LocalDate;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.Comparator;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
-import java.util.Set;
-import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.LinkedHashMap;
 import lombok.RequiredArgsConstructor;
@@ -92,10 +88,12 @@ public CreateChallengeResponseDto createChallenge(CreateChallengeRequestDto requ
     }
 
     // 5. 이메일 전송 & 정보 저장
-    for (String email : requestDto.getEmailList()) {
-      emailService.sendEmail(challenge, email);
-      emailRepository.save(new Email(email, challenge));
-    }
+    emailService.sendEmail(challenge, requestDto.getEmailList());
+
+    List<Email> emailEntities = requestDto.getEmailList().stream()
+        .map(email -> new Email(email, challenge))
+        .collect(Collectors.toList());
+    emailRepository.saveAll(emailEntities);
 
     // 6. Response 생성
     List<Challenge> challenges = challengeRepository.findByOrganizationId(organization.getId());
@@ -132,7 +130,7 @@ public List<UserStatus> getDashboard(Long challengeId) {
     for (UserChallenge userChallenge : userChallengeList) {
       List<Status> statusList = new ArrayList<>();
       List<UserTemplate> userTemplateList = userTemplateRepository.findByUserChallengeId(
-              userChallenge.getId());
+          userChallenge.getId());
 
       for (ChallengeDay challengeDay : challengeDayList) {
         // 참여여부 확인과정
diff --git a/src/main/java/com/writon/admin/domain/service/EmailService.java b/src/main/java/com/writon/admin/domain/service/EmailService.java
index a8c4272..14c8044 100644
--- a/src/main/java/com/writon/admin/domain/service/EmailService.java
+++ b/src/main/java/com/writon/admin/domain/service/EmailService.java
@@ -5,70 +5,84 @@
 import com.writon.admin.domain.util.TokenUtil;
 import com.writon.admin.global.error.CustomException;
 import com.writon.admin.global.error.ErrorCode;
-import jakarta.mail.internet.MimeMessage;
 import java.net.URLEncoder;
 import java.nio.charset.StandardCharsets;
-import org.thymeleaf.context.Context;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
-import org.springframework.mail.javamail.JavaMailSender;
-import org.springframework.mail.javamail.MimeMessageHelper;
-import org.springframework.scheduling.annotation.Async;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.stereotype.Service;
-import org.thymeleaf.spring6.SpringTemplateEngine;
+import sendinblue.ApiClient;
+import sendinblue.ApiException;
+import sendinblue.Configuration;
+import sendinblue.auth.ApiKeyAuth;
+import sibApi.TransactionalEmailsApi;
+import sibModel.CreateSmtpEmail;
+import sibModel.SendSmtpEmail;
+import sibModel.SendSmtpEmailMessageVersions;
+import sibModel.SendSmtpEmailTo1;
 
 @Service
 @RequiredArgsConstructor
 @Slf4j
 public class EmailService {
 
-  private final JavaMailSender javaMailSender;
-  private final SpringTemplateEngine templateEngine;
   private final TokenUtil tokenUtil;
 
-  @Async
-  public void sendEmail(Challenge challenge, String email) {
-    MimeMessage mimeMessage = javaMailSender.createMimeMessage();
+  @Value("${email.apiKey}")
+  private String BREVO_API_KEY;
+
+  @Value("${email.templateId}")
+  private Long BREVO_TEMPLATE_ID;
+
+  public void sendEmail(Challenge challenge, List<String> emailList) {
     Organization organization = tokenUtil.getOrganization();
+    String baseUrl = "https://www.writon.co.kr/login";
+    String link = String.format(
+        "%s?organization=%s&challengeId=%s", baseUrl,
+        encodeURIComponent(organization.getName()),
+        encodeURIComponent(String.valueOf(challenge.getId()))
+    );
 
-    try {
-      MimeMessageHelper mimeMessageHelper = new MimeMessageHelper(mimeMessage, false, "UTF-8");
-      mimeMessageHelper.setTo(email);
-      mimeMessageHelper.setSubject(String.format(
-          "[Writon] %s의 챌린지에 참여해보세요",
-          organization.getName()
-      )); // 메일 제목
-      mimeMessageHelper.setText(
-          setContext(organization.getName(), challenge.getName(), challenge.getId(), email),
-          true
-      ); // 메일 본문 내용, HTML 여부
-      javaMailSender.send(mimeMessage);
+    ApiClient defaultClient = Configuration.getDefaultApiClient();
 
-      log.info("Succeeded to send Email");
-    } catch (Exception e) {
-      log.info("Failed to send Email");
-      throw new CustomException(ErrorCode.EMAIL_SEND_FAILED);
-    }
-  }
+    ApiKeyAuth apiKey = (ApiKeyAuth) defaultClient.getAuthentication("api-key");
+    apiKey.setApiKey(BREVO_API_KEY);
 
-  //thymeleaf를 통한 html 적용
-  public String setContext(String organization, String challenge, Long challengeId, String email) {
-    Context context = new Context();
-    context.setVariable("organization", organization);
-    context.setVariable("challenge", challenge);
-    context.setVariable("email", email);
-    context.setVariable("challengeId", challengeId);
+    // 수신자 리스트 구성
+    List<SendSmtpEmailMessageVersions> messageVersions = new ArrayList<>();
 
-    String baseUrl = "https://www.writon.co.kr/login";
-    String link = String.format("%s?organization=%s&challengeId=%s", baseUrl,
-        encodeURIComponent(organization),
-        encodeURIComponent(String.valueOf(challengeId)));
-    context.setVariable("link", link);
+    for (String email : emailList) {
+      messageVersions.add(new SendSmtpEmailMessageVersions()
+          .to(List.of(new SendSmtpEmailTo1().email(email)))
+          .params(Map.of(
+              "ORGANIZATION", organization.getName(),
+              "CHALLENGE", challenge.getName(),
+              "EMAIL", email,
+              "LINK", link
+          )));
+    }
 
-    return templateEngine.process("participate_card", context);
+    TransactionalEmailsApi apiInstance = new TransactionalEmailsApi();
+    SendSmtpEmail sendSmtpEmail = new SendSmtpEmail()
+        // 템플릿 종류
+        .templateId(BREVO_TEMPLATE_ID)
+        // 동적 param값 설정
+        .messageVersions(messageVersions);
+
+    try {
+      CreateSmtpEmail result = apiInstance.sendTransacEmail(sendSmtpEmail);
+      log.info("Succeded to send Email: {}", result);
+    } catch (ApiException e) {
+      log.error("Failed to send Email");
+      throw new CustomException(ErrorCode.EMAIL_SEND_FAILED);
+    }
   }
 
   private String encodeURIComponent(String value) {
     return URLEncoder.encode(value, StandardCharsets.UTF_8);
   }
-}
+
+}
\ No newline at end of file
diff --git a/src/main/java/com/writon/admin/domain/service/OrganizationService.java b/src/main/java/com/writon/admin/domain/service/OrganizationService.java
index 008d005..e900bef 100644
--- a/src/main/java/com/writon/admin/domain/service/OrganizationService.java
+++ b/src/main/java/com/writon/admin/domain/service/OrganizationService.java
@@ -7,7 +7,6 @@
 import com.writon.admin.domain.entity.organization.AdminUser;
 import com.writon.admin.domain.entity.organization.Organization;
 import com.writon.admin.domain.entity.organization.Position;
-import com.writon.admin.domain.repository.organization.AdminUserRepository;
 import com.writon.admin.domain.repository.organization.OrganizationRepository;
 import com.writon.admin.domain.repository.organization.PositionRepository;
 import com.writon.admin.domain.util.TokenUtil;
diff --git a/src/main/java/com/writon/admin/domain/service/ParticipationService.java b/src/main/java/com/writon/admin/domain/service/ParticipationService.java
index f6da23e..5dc5259 100644
--- a/src/main/java/com/writon/admin/domain/service/ParticipationService.java
+++ b/src/main/java/com/writon/admin/domain/service/ParticipationService.java
@@ -116,10 +116,12 @@ public List<String> participate(Long challengeId, List<String> emailList) {
     Challenge challenge = challengeRepository.findById(challengeId)
         .orElseThrow(() -> new CustomException(ErrorCode.CHALLENGE_NOT_FOUND));
 
-    for (String email : emailList) {
-      emailService.sendEmail(challenge, email);
-      emailRepository.save(new Email(email, challenge));
-    }
+    emailService.sendEmail(challenge, emailList);
+
+    List<Email> emailEntities = emailList.stream()
+        .map(email -> new Email(email, challenge))
+        .collect(Collectors.toList());
+    emailRepository.saveAll(emailEntities);
 
     List<Email> sendedEmailList = emailRepository.findByChallengeId(challengeId);
     if (sendedEmailList.isEmpty()) {
diff --git a/src/main/java/com/writon/admin/global/error/ErrorCode.java b/src/main/java/com/writon/admin/global/error/ErrorCode.java
index 4d232e3..10219e7 100644
--- a/src/main/java/com/writon/admin/global/error/ErrorCode.java
+++ b/src/main/java/com/writon/admin/global/error/ErrorCode.java
@@ -17,6 +17,7 @@ public enum ErrorCode {
   METHOD_NOT_ALLOWED(HttpStatus.METHOD_NOT_ALLOWED, "405", "허용되지 않은 메소드입니다"), // 405 Method Not Allowed
   CONFLICT(HttpStatus.CONFLICT, "409", "이미 가입한 사용자입니다"), // 409 Conflict
   INTERNAL_SERVER_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "500", "서버에 오류가 발생하였습니다"), // 500 Internal Server Error
+  GATEWAY_TIMEOUT_ERROR(HttpStatus.GATEWAY_TIMEOUT, "504", "연결 시간을 초과하였습니다"), // 503 Gateway Timeout
   ETC_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "0314", "사용자 지정 오류"),
 
   // auth
diff --git a/src/main/resources/.gitkeep b/src/main/resources/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/src/main/resources/templates/participate_card.html b/src/main/resources/templates/participate_card.html
deleted file mode 100644
index fe503e2..0000000
--- a/src/main/resources/templates/participate_card.html
+++ /dev/null
@@ -1,38 +0,0 @@
-<!DOCTYPE html>
-<html xmlns:th="http://www.thymeleaf.org">
-
-<body>
-<table role="presentation" cellspacing="0" cellpadding="0" border="0" width="100%">
-  <tr>
-    <td style="text-align: center;">
-      <img
-          src="https://writon-data2.s3.ap-northeast-2.amazonaws.com/invitation/%EC%B4%88%EB%8C%80%EC%9E%A5+2.0.png"
-          alt="Your Image"
-          style="display: block; margin: 0 auto; margin-bottom: 16px; width: 500px; height: 500px;">
-    </td>
-  </tr>
-  <tr>
-    <td style="text-align: center;">
-      <p style="font-size: 18px; color: #333; white-space: pre-line; line-height: 0.7;  margin-bottom: 10px;">
-        <strong style="font-weight: bold;">[[${organization}]]</strong>에서 [[${email}]]님을 <br>
-        <strong style="font-weight: bold;">[[${challenge}]]</strong> 챌린지로 초대하였습니다<br>
-      </p>
-    </td>
-  </tr>
-  <tr>
-    <td style="text-align: center;">
-      <a th:href="@{${link}}"
-         style="display: block; text-align: center;"
-         target="_blank"
-         data-saferedirecturl="[[https://www.google.com/url?q=${link}]]">
-        <img
-            src="https://writon-data2.s3.ap-northeast-2.amazonaws.com/invitation/%EC%B4%88%EB%8C%80%EC%9E%A5+%EB%B2%84%ED%8A%BC+2.0.png"
-            alt="Your Button Image"
-            style="display: block; margin: 0 auto; width: 347px; height: 105px;">
-      </a>
-    </td>
-  </tr>
-</table>
-
-</body>
-</html>
\ No newline at end of file