使用javax.mail发送Gmail无送达及认证失败问题排查

我用Kotlin开发Android应用，通过javax.mail包用Gmail账号发送邮件。调用sendEmail方法后邮件无送达，同时抛出javax.mail.AuthenticationFailedException: 535-5.7.8 Username and Password not accepted错误。想解决三个问题：

1. 是否需要开启Gmail两步验证？
2. 代码本身有没有问题？
3. 如何修复这个认证失败的错误？

以下是Notify.kt完整代码：

package com.facecool.utils

import android.graphics.Bitmap
import java.io.ByteArrayOutputStream
import java.util.Properties
import javax.activation.DataHandler
import javax.activation.DataSource
import javax.mail.Authenticator
import javax.mail.Message
import javax.mail.Multipart
import javax.mail.Part
import javax.mail.PasswordAuthentication
import javax.mail.Session;
import javax.mail.Transport
import javax.mail.internet.InternetAddress
import javax.mail.internet.MimeBodyPart
import javax.mail.internet.MimeMessage
import javax.mail.internet.MimeMultipart
import javax.mail.util.ByteArrayDataSource


internal object Notify {
    fun sendEmail(
        subject: String?,
        message: String?,
        recipientEmail: String?,
        bmp: Bitmap?
    ) {
        if (recipientEmail == null || recipientEmail.isEmpty()) return
        try {
            val yourMail = "example@gmail.com"
            val yourPwd = "password"
            val properties = getProperties()
            properties["mail.debug"] = "false"

            // Create a session with authentication
            val session: Session = Session.getInstance(properties, object : Authenticator() {
                override fun getPasswordAuthentication(): PasswordAuthentication {
                    return PasswordAuthentication(
                        yourMail,
                        yourPwd
                    )
                }
            })

                val mimeMessage: MimeMessage? = createMimeMessage(
                    session, yourMail, recipientEmail, subject, message,
                    bmp!!
                )
                Transport.send(mimeMessage)
        } catch (e: java.lang.Exception) {
 
            e.printStackTrace()
        }
    }
    fun getProperties(): Properties {

        val properties = Properties()
  
            properties.put("mail.smtp.host", "smtp.gmail.com")
            properties.put("mail.smtp.port", "587")
            properties.put("mail.smtp.starttls.enable", "true")
            properties.put("mail.smtp.auth", "true")
            properties.put("mail.smtp.ssl.trust", "smtp.gmail.com")
        
        return properties
    }
    
    private fun getImageData(bmp: Bitmap): ByteArray? {
        val byteArrayOutputStream = ByteArrayOutputStream()
        bmp.compress(Bitmap.CompressFormat.JPEG, 100, byteArrayOutputStream)
        return byteArrayOutputStream.toByteArray()
    }
    
    fun createMimeMessage(
        session: Session?,
        yourMail: String,
        recipientEmail: String,
        subject: String?,
        message: String?,
        bmp: Bitmap
    ): MimeMessage? {
        try {
            val mimeMessage = MimeMessage(session)
            mimeMessage.setFrom(InternetAddress(yourMail))
            if (!recipientEmail.isEmpty()) mimeMessage.setRecipient(
                Message.RecipientType.TO,
                InternetAddress(recipientEmail)
            )
            mimeMessage.setSubject(subject)

            // Add text part to the multipart
            val multipart: Multipart = MimeMultipart("mixed")
            val textPart = MimeBodyPart()
            textPart.setText(message)
            multipart.addBodyPart(textPart)
            
            //add Recognized Image
            val filePart = MimeBodyPart()
            filePart.setFileName("Recognized Face.jpg")
            filePart.setDisposition(Part.ATTACHMENT)
            val source: DataSource = ByteArrayDataSource(getImageData(bmp), "image/jpeg")
            filePart.setDataHandler(DataHandler(source))
            multipart.addBodyPart(filePart)
            
            //end
            mimeMessage.setContent(multipart)
            return mimeMessage
        } catch (e: Exception) {
            e.printStackTrace()
        }
        return null
    }
}

1. 是否需要开启Gmail两步验证？ #

不是强制要求，但更推荐开启：

• 开启两步验证后，必须使用「应用专用密码」登录SMTP，这比直接用账号密码更安全，且能避开Gmail对普通密码登录SMTP的限制；
• 如果不开启两步验证，Gmail的「不太安全的应用访问」选项已逐步淘汰，大部分账号无法通过普通密码登录SMTP。

2. 代码存在的问题 #

• 硬编码密码：直接写死yourPwd = "password"，既不安全，也不符合当前Gmail的认证规则；
• 空值处理隐患：bmp!!强制非空，调用时传入null会直接崩溃；
• 调试日志关闭：mail.debug=false关闭了SMTP交互日志，不利于排查认证细节；
• 异常处理简陋：仅打印堆栈，没有针对认证失败的反馈逻辑；
• 空值未兜底：subject、message未设置默认值，可能导致邮件内容异常。

3. 错误修复步骤 #

方案一：两步验证+应用专用密码（推荐） #

1. 登录Gmail账号，开启两步验证；
2. 进入Google账号「安全」设置，生成应用专用密码（选择「邮件」应用，设备选「其他」）；
3. 将代码中的yourPwd替换为这个应用专用密码。

方案二：代码修复建议 #

internal object Notify {
    fun sendEmail(
        subject: String?,
        message: String?,
        recipientEmail: String?,
        bmp: Bitmap?
    ) {
        // 提前拦截空值，避免后续崩溃
        if (recipientEmail.isNullOrEmpty() || bmp == null) return
        try {
            val yourMail = "your-real-email@gmail.com"
            // 替换为生成的应用专用密码
            val yourAppPassword = "your-app-specific-password"
            val properties = getProperties()
            properties["mail.debug"] = "true" // 开启调试日志，方便排查问题

            val session: Session = Session.getInstance(properties, object : Authenticator() {
                override fun getPasswordAuthentication(): PasswordAuthentication {
                    return PasswordAuthentication(yourMail, yourAppPassword)
                }
            })

            // 空值判断，避免空指针
            createMimeMessage(session, yourMail, recipientEmail, subject, message, bmp)?.let {
                Transport.send(it)
            }
        } catch (e: Exception) {
            e.printStackTrace()
            // 可添加错误回调，通知上层逻辑认证失败
        }
    }

    fun getProperties(): Properties {
        val properties = Properties()
        properties.put("mail.smtp.host", "smtp.gmail.com")
        properties.put("mail.smtp.port", "587")
        properties.put("mail.smtp.starttls.enable", "true")
        properties.put("mail.smtp.auth", "true")
        properties.put("mail.smtp.ssl.trust", "smtp.gmail.com")
        return properties
    }

    // 去掉可空返回，因为bmp已经提前做非空判断
    private fun getImageData(bmp: Bitmap): ByteArray {
        val byteArrayOutputStream = ByteArrayOutputStream()
        bmp.compress(Bitmap.CompressFormat.JPEG, 100, byteArrayOutputStream)
        return byteArrayOutputStream.toByteArray()
    }

    fun createMimeMessage(
        session: Session?,
        yourMail: String,
        recipientEmail: String,
        subject: String?,
        message: String?,
        bmp: Bitmap
    ): MimeMessage? {
        return try {
            val mimeMessage = MimeMessage(session)
            mimeMessage.setFrom(InternetAddress(yourMail))
            mimeMessage.setRecipient(Message.RecipientType.TO, InternetAddress(recipientEmail))
            // 给subject设置默认值，避免空指针
            mimeMessage.subject = subject ?: "无主题"

            val multipart: Multipart = MimeMultipart("mixed")
            val textPart = MimeBodyPart()
            // 给message设置默认值
            textPart.setText(message ?: "")
            multipart.addBodyPart(textPart)

            val filePart = MimeBodyPart()
            filePart.fileName = "Recognized Face.jpg"
            filePart.disposition = Part.ATTACHMENT
            val source: DataSource = ByteArrayDataSource(getImageData(bmp), "image/jpeg")
            filePart.dataHandler = DataHandler(source)
            multipart.addBodyPart(filePart)

            mimeMessage.setContent(multipart)
            mimeMessage
        } catch (e: Exception) {
            e.printStackTrace()
            null
        }
    }
}

额外注意事项 #

• 检查设备网络是否能访问Gmail的SMTP服务器（端口587是否被防火墙/代理拦截）；
• 开启mail.debug=true后，查看控制台输出的SMTP交互日志，确认认证失败的具体细节；
• 确保Gmail账号没有开启严格的安全浏览限制。

内容的提问来源于stack exchange，提问作者saas