======External Message Store Scripting======
Added in VPOP3 Enterprise v9.1

This allows some messages to be stored in an external message store somewhere, accessed via S3, SFTP or similar

====DownloadFromExternal====
  function DownloadFromExternal(MsgDataId, ExtData, TargetFileName)
  
returns <success>, <new ExtData or Error Text>

====GetMessagesToMoveToExternal====
  function GetMessagesToMoveToExternal()
  
returns <table of MsgDataIDs>

====UploadToExternal====
  function UploadToExternal(MsgDataId, SourceFileName)
  
returns <success>, <new ExtData or Error Text>
  
====DeleteFromExternal====
  function DeleteFromExternal(MsgDataId)
  
returns <success>, <new ExtData or Error Text>

====GetMessagesToMoveFromExternal====
  function GetMessagesToMoveFromExternal()
  
returns <table of MsgDataIDs>

====GetTidyLocalHours====
  function GetTidyLocalHours(MaxAgeHours, MaxTidyCount)
  
returns MaxAgeHours, MaxTidyCount

Tells VPOP3 how long locally cached message files should be kept, and how many should be deleted per iteration around the management loop


====GetNextIterationDelay====
  function GetNextIterationDelay(ActionResults, Delay)
 
returns <new delay in milliseconds>

====Example====

<code lua>
url = "https://s3.eu-central-1.wasabisys.com";
bucket = "<bucket name>";
accesskey = "<access key>";
secretkey = "<secret key>";
prefix = "extstore/";

function GetMessagesToMoveToExternal()
    local x = VPOP3.PostgresQuery("SELECT msgdataid FROM messages.msgdata WHERE NOT extmsg ORDER by msgdataid limit 1;")
    if x.Rows > 0 then
        return {x[1]["msgdataid"]}
    else
        return {}
    end
end

function DownloadFromExternal(msgid, data, filename)
    ret,retstr = VPOP3Net.S3Get(url, bucket, accesskey, secretkey, prefix .. msgid, filename);
    
    if ret == 0 then
        return true, data
    else
        return false, retstr
    end
    
end


function UploadToExternal(msgid, filename)
    ret,retstr = VPOP3Net.S3Put(url, bucket, accesskey, secretkey, prefix .. msgid, filename);
    
    if ret == 0 then
        return true, "abc"
    else
        return false, retstr
    end
    
end

function DeleteFromExternal(msgid)
    ret,retstr = VPOP3Net.S3Delete(url, bucket, accesskey, secretkey, prefix .. msgid);
    
    if ret == 0 then
        return true, "abc"
    else
        return false, retstr
    end
end

function GetTidyLocalHours(h, c)
    return 5, 1
end

function GetNextIterationDelay(r, d)
    return 10000;
end
</code>