chore: add anti spamming and headers to email send

src/modules/email/email.controller.ts

@@ -16,9 +16,13 @@ export class EmailController {
   constructor(private readonly emailService: EmailService) {}
 
   @Post("send")
-  @ApiOperation({ summary: "Send an email" })
+  @ApiOperation({
+    summary: "Send an email with configurable headers based on type",
+    description:
+      "Send emails with automatic anti-threading and anti-spam headers. Supports different email types: general, transactional, marketing, anti-threading. Marketing emails require listId and unsubscribeUrl.",
+  })
   @ApiResponse({ status: 201, description: "Email sent successfully" })
-  @ApiResponse({ status: 400, description: "Invalid email data" })
+  @ApiResponse({ status: 400, description: "Invalid email data or missing required fields for email type" })
   @ApiResponse({ status: 403, description: "Not authorized to send email" })
   sendEmail(@UserDec("wildduckUserId") userEmailId: string, @Body() sendEmailDto: SendEmailDto) {
     return this.emailService.sendEmail(userEmailId, sendEmailDto);