[void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")

#SharePoint variables

$SiteUrl = "http://siteurl"

$WebUrl = "weburl"

$LibraryName = "listname"

#Save Path

$SavePath = "C:\ListBackup20200227"

#Get SPSite

$site= New-Object Microsoft.SharePoint.SPSite($SiteUrl)

#Get SPWeb

$Web = $site.OpenWeb($WebUrl)

#Get SPList

$List = $Web.Lists[$LibraryName]

#Loop SPListItem. If SPFolder, skip the item

foreach ($ListItem in $List.Items){

    #Set SavePath

    $SaveFolder = $SavePath + "\" + $ListItem.ID 

    #Check if SavePath exists already. If not, create SavePath

    if (!(Test-Path -path $SaveFolder)){  

        New-Item $SaveFolder -type directory

    }

    #Get all SPAttachment

    $AttachmentsColl = $ListItem.Attachments

    #Loop all SPAttachment

    foreach ($Attachment in $AttachmentsColl){

        #Get attachment

        $file = $web.GetFile($listItem.Attachments.UrlPrefix + $Attachment)

        $bytes = $file.OpenBinary()

        #Save attachment

        $FilePath = $SaveFolder + " \" + $Attachment

        $fs = new-object System.IO.FileStream($FilePath, "OpenOrCreate")

        $fs.Write($bytes, 0 , $bytes.Length)

        $fs.Close()

    }

}