在Flutter中集成Mandrill邮件发送功能通常需要借助其API。由于Flutter本身不直接提供邮件发送功能，我们需要使用网络请求库（如http包）来与Mandrill的API进行交互。以下是一个基本的示例代码，展示如何在Flutter应用中通过Mandrill发送邮件。

首先，确保你已经注册了Mandrill账号，并获取了API密钥。

步骤 1: 添加依赖

在你的pubspec.yaml文件中添加http依赖：

dependencies:
  flutter:
    sdk: flutter
  http: ^0.13.3  # 请检查最新版本号

然后运行flutter pub get来安装依赖。

步骤 2: 编写邮件发送逻辑

创建一个Dart文件（例如mandrill_service.dart），并在其中编写发送邮件的逻辑。

import 'dart:convert';
import 'package:http/http.dart' as http;

class MandrillService {
  final String apiKey;

  MandrillService({required this.apiKey});

  Future<void> sendEmail({
    required String toEmail,
    required String subject,
    required String text,
    String? html,
    List<Map<String, String>>? mergeVars,
    Map<String, dynamic>? async,
    Map<String, dynamic>? ip_pool,
    String? send_at,
    List<String>? tags,
    Map<String, dynamic>? subaccount,
    String? return_path_domain,
    bool? signing_domain,
    bool? auto_text,
    bool? auto_html,
    bool? merge,
    bool? validate,
    bool? track_opens,
    bool? track_clicks,
    bool? url_strip_qs,
    bool? preserve_recipients,
    bool? view_content_link,
    String? bcc_address,
    bool? tracking_domain,
    bool? canonical_identifiers,
    bool? inline_css,
    bool? google_analytics_domains,
    bool? google_analytics_campaign,
    bool? metadata,
    String? recipient_metadata,
    bool? from_name,
    bool? reply_to,
    bool? to_name,
    bool? headers,
    bool? important,
    bool? mirror,
    bool? smtp_envelope,
    bool? return_path,
    bool? signing_domain_signature,
    bool? merge_language,
  }) async {
    final url = Uri.parse('https://mandrillapp.com/api/1.0/messages/send.json');

    final body = {
      'key': apiKey,
      'message': {
        'html': html,
        'text': text,
        'subject': subject,
        'from_email': 'your-email@example.com', // 发件人邮箱
        'to': [
          {'email': toEmail, 'name': '', 'type': 'to'},
        ],
        'merge_vars': mergeVars ?? [],
        'auto_text': auto_text ?? false,
        'auto_html': auto_html ?? null,
        'async': async ?? false,
        'ip_pool': ip_pool ?? null,
        'send_at': send_at,
        'tags': tags ?? [],
        'subaccount': subaccount ?? null,
        'return_path_domain': return_path_domain,
        'signing_domain': signing_domain ?? null,
        'track_opens': track_opens ?? null,
        'track_clicks': track_clicks ?? null,
        'url_strip_qs': url_strip_qs ?? null,
        'preserve_recipients': preserve_recipients ?? null,
        'view_content_link': view_content_link ?? null,
        'bcc_address': bcc_address,
        'tracking_domain': tracking_domain ?? null,
        'canonical_identifiers': canonical_identifiers ?? null,
        'inline_css': inline_css ?? null,
        'google_analytics_domains': google_analytics_domains ?? null,
        'google_analytics_campaign': google_analytics_campaign ?? null,
        'metadata': metadata ?? null,
        'recipient_metadata': recipient_metadata,
        'headers': headers ?? null,
        'important': important ?? null,
        'mirror': mirror ?? null,
        'smtp_envelope': smtp_envelope ?? null,
        'return_path': return_path ?? null,
        'signing_domain_signature': signing_domain_signature ?? null,
        'merge_language': merge_language ?? null,
      },
      'async': merge ?? false,
      'validate': validate ?? false,
    };

    final response = await http.post(
      url,
      body: jsonEncode(body),
      headers: {
        'Content-Type': 'application/json',
      },
    );

    if (response.statusCode != 200) {
      throw Exception('Failed to send email: ${response.body}');
    }

    print('Email sent successfully: ${response.body}');
  }
}

步骤 3: 使用邮件发送服务

在你的Flutter应用中，你可以这样使用MandrillService来发送邮件：

import 'package:flutter/material.dart';
import 'mandrill_service.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Send Email with Mandrill'),
        ),
        body: Center(
          child: ElevatedButton(
            onPressed: () async {
              final mandrillService = MandrillService(apiKey: 'your-mandrill-api-key');
              try {
                await mandrillService.sendEmail(
                  toEmail: 'recipient@example.com',
                  subject: 'Test Email',
                  text: 'This is a test email sent from Flutter using Mandrill.',
                  // html: '<h1>Test Email</h1><p>This is a test email sent from Flutter using Mandrill.</p>',
                );
                ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Email sent successfully')));
              } catch (e) {
                ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to send email: $e')));
              }
            },
            child: Text('Send Email'),
          ),
        ),
      ),
    );
  }
}

请注意，上面的代码示例仅用于演示目的。在实际应用中，你应该避免在客户端代码中硬编码API密钥，而是应该考虑使用更安全的方法（如后端服务）来处理敏感信息。同时，确保遵守所有相关的隐私和安全最佳实践。