refactor : 메일 전송 비동기로 보내도록 변경

likelion-client/src/main/java/likelion/univ/LikelionClientApplication.java

@@ -3,12 +3,10 @@
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.cache.annotation.EnableCaching;
-import org.springframework.scheduling.annotation.EnableAsync;
 import org.springframework.scheduling.annotation.EnableScheduling;
 
 @EnableCaching
 @EnableScheduling
-@EnableAsync
 @SpringBootApplication
 public class LikelionClientApplication {
 

likelion-client/src/main/java/likelion/univ/hackathon/email/HackathonApplyEmailContent.java

@@ -16,7 +16,7 @@ public final class HackathonApplyEmailContent {
             				<tr>
             					<td style="width: 20px"></td>
             					<td>
-            						<img src="https://drive.google.com/uc?id=17_m34Zn_PnbB_R5HjzJJe0k1Lh4BX04w" width="300" height="100" style="max-width: 100%; height: auto; vertical-align: top">
+            						<img src="https://drive.google.com/thumbnail?id=17_m34Zn_PnbB_R5HjzJJe0k1Lh4BX04w&sz=s4000" width="300" height="100" style="max-width: 100%; height: auto; vertical-align: top" loading="eager">
             					</td>
             				</tr>
             				<tr>

likelion-core/src/main/java/likelion/univ/config/AsyncConfig.java

@@ -0,0 +1,23 @@
+package likelion.univ.config;
+
+import java.util.concurrent.Executor;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.scheduling.annotation.EnableAsync;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+
+@Configuration
+@EnableAsync
+public class AsyncConfig {
+
+    @Bean(name = "threadPoolTaskExecutor")
+    public Executor threadPoolTaskExecutor() {
+        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
+        executor.setCorePoolSize(5);
+        executor.setMaxPoolSize(30);
+        executor.setQueueCapacity(50);
+        executor.setThreadNamePrefix("LIKELION_ASYNC");
+        executor.initialize();
+        return executor;
+    }
+}

likelion-infrastructure/src/main/java/likelion/univ/email/sender/azure/AzureEmailSender.java

@@ -19,6 +19,7 @@
 import likelion.univ.email.sender.EmailContent;
 import likelion.univ.email.sender.EmailSender;
 import lombok.RequiredArgsConstructor;
+import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Component;
 import org.springframework.web.multipart.MultipartFile;
 
@@ -28,6 +29,7 @@ public class AzureEmailSender implements EmailSender {
 
     private final AzureCommunicationProperties properties;
 
+    @Async
     @Override
     public void send(EmailContent emailContent) {
         EmailClient emailClient = setUpEmailClient();