PowerShell发送带附件邮件：单收件人正常，多收件人延迟/失败

问题现象 #

发送单个收件人时，邮件及附件可在1分钟内正常送达；但发送8个收件人时，邮件需30分钟以上才能送达，甚至直接发送失败。执行代码如下：

# Send the email
$rec1 = "someone1@someone.com"
$recipients = @(
"someone1@someone.com"
"someone2@someone.comm"
"someone3@someone.com"
"someone4@someone.com"
"someone5@someone.comm"
"someone6@someone.com"
"someone7@someone.com"
"someone8@someone.com"
)

# Set email parameters
$smtpServer = "myaddress"
$smtpFrom = $rec1
$smtpTo = $recipients
$messageSubject = "Subject Placeholder"
$messageBody = "Hi, forecast is attached."
# Get the latest file in the folder
$folderPath = "C:\Users\Forecast"
$latestFile = Get-ChildItem $folderPath | Sort-Object LastWriteTime -Descending | Select-Object -First 1
# Set attachment parameters
$attachmentPath = $latestFile.FullName
$attachmentName = $latestFile.Name
# Create and send the email
$mailmessage = New-Object system.net.mail.mailmessage
$mailmessage.from = ($smtpFrom)
$mailmessage.To.add($smtpTo)
$mailmessage.Subject = $attachmentName
$mailmessage.Body = $messageBody
# Attach the latest file
$attachment = New-Object Net.Mail.Attachment($attachmentPath)
$mailmessage.Attachments.Add($attachment)
# Set email client
$smtp = New-Object Net.Mail.SmtpClient($smtpServer)
# Send email
$smtp.Send($mailmessage)
# Dispose of the attachment
$attachment.Dispose()

问题原因 #

• 收件人地址拼写错误：代码中someone2@someone.comm和someone5@someone.comm的域名后缀为.comm（正确应为.com），SMTP服务器会反复尝试投递错误地址，引发重试延迟，甚至触发服务器限流机制。
• 收件人添加方式不当：直接将数组传入$mailmessage.To.add()，部分SMTP服务器无法正确解析批量地址，导致投递流程异常。
• 无超时设置与错误捕获：默认SMTP客户端超时时间过长，若服务器处理缓慢会持续等待，最终可能超时失败且无法定位问题。
• 服务器批量发送限制：部分SMTP服务器对单次发送的收件人数量、频率有管控，超过阈值会被限流或延迟处理。

解决方案 #

1. 修正所有错误的收件人邮箱地址，确保格式合规。
2. 循环遍历收件人列表，逐个添加到邮件对象，避免批量解析问题。
3. 为SMTP客户端设置合理超时时间，并添加错误捕获逻辑，便于排查投递问题。
4. 若服务器有批量发送限制，可拆分收件人列表分批次发送。
5. 完整释放邮件对象和附件资源，避免资源占用引发异常。

修正后的代码示例 #

# 定义收件人列表（修正错误域名）
$recipients = @(
    "someone1@someone.com",
    "someone2@someone.com",
    "someone3@someone.com",
    "someone4@someone.com",
    "someone5@someone.com",
    "someone6@someone.com",
    "someone7@someone.com",
    "someone8@someone.com"
)

# 邮件参数配置
$smtpServer = "myaddress"
$smtpFrom = "someone1@someone.com"
$messageSubject = "Subject Placeholder"
$messageBody = "Hi, forecast is attached."

# 获取文件夹中最新文件
$folderPath = "C:\Users\Forecast"
$latestFile = Get-ChildItem $folderPath | Sort-Object LastWriteTime -Descending | Select-Object -First 1
$attachmentPath = $latestFile.FullName

# 创建并发送邮件
try {
    $mailmessage = New-Object System.Net.Mail.MailMessage
    $mailmessage.From = $smtpFrom
    
    # 循环添加收件人
    foreach ($recipient in $recipients) {
        $mailmessage.To.Add($recipient)
    }
    
    $mailmessage.Subject = $latestFile.Name
    $mailmessage.Body = $messageBody
    
    # 添加附件
    $attachment = New-Object Net.Mail.Attachment($attachmentPath)
    $mailmessage.Attachments.Add($attachment)
    
    # 配置SMTP客户端，设置30秒超时
    $smtp = New-Object Net.Mail.SmtpClient($smtpServer)
    $smtp.Timeout = 30000
    
    # 发送邮件
    $smtp.Send($mailmessage)
    Write-Host "邮件发送成功"
}
catch {
    Write-Error "邮件发送失败: $_"
}
finally {
    # 释放所有资源
    if ($attachment) { $attachment.Dispose() }
    if ($mailmessage) { $mailmessage.Dispose() }
    if ($smtp) { $smtp.Dispose() }
}

内容的提问来源于stack exchange，提问作者Knockoutpie