Multiple mails can not be sent at (exactely) the same time

[GoogleCodeExporter]

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=== PLEASE READ BEFORE FILING ISSUE:
https://code.google.com/p/gmail-delay-send/wiki/GmailDelaySendDebugging_8
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What steps will reproduce the problem?
1.Make multiple (more than 1) mails
2. put same date and time in ALL those mail f.e. @2014-06-06 10:15:00
3.Apply the GmailDelaySend/ToSend label

What is the expected output? What do you see instead?
Expected is that all those mails would be sent at the same time, but at the due 
time an errormail is sent and the mails remain unsent

What version of the product are you using?
Script Version: 8 

Please provide any additional information below.
When the date and time are not exactely the same, it works fine.
f.e.:
mail1: @2014-06-06 10:15:01
mail2: @2014-06-06 10:15:02
mail3: @2014-06-06 10:15:03
...

This is the error message when exactely the same date and time are used:

-- Error:Error: Gmail Delay Send failed to connect to one of the Google 
Services. This is OK if it happens infrequently, the script will run again in a 
few minutes. See here to avoid receiving these notifications: 
https://code.google.com/p/gmail-delay-send/wiki/GmailDelaySendOptions_8#Error_No
tifications. Function being called: function () { GmailApp.sendEmail(to, 
subject, body, {htmlBody:htmlBody, cc:cc, bcc:bcc, from:from, 
attachments:attach, name:name}); } .Error message: Exception: Ongeldig 
argument: --Stack: at Services (GmailDelaySendWeb):209 (executeCommand) at 
Services (GmailDelaySendWeb):107 (serviceSendEmailMessage) at Mail 
(GmailDelaySendWeb):66 (sendMessage) at Main (GmailDelaySendWeb):160 
(tryToSendMessage) at Main (GmailDelaySendWeb):188 (processThread) at Main 
(GmailDelaySendWeb):206 (processThreads) at Main (GmailDelaySendWeb):24 (main) 

Original issue reported on code.google.com by frankyva...@gmail.com on 6 Jun 2014 at 8:11

[GoogleCodeExporter]

An update after some more tests.
It seems that these errors occur when multiple mails are set to be sent within 
a same interval of a trigger:
example:
mail1: @2014-06-06 10:15
mail2: @2014-06-06 10:16
mail3: @2014-06-06 10:17
When the trigger is set to 10 minutes they are not sent, the above error 
message is given.
When the trigger is set to 1 minute, the mails are sent one by one in the 
respective time frame.

Original comment by frankyva...@gmail.com on 11 Jun 2014 at 12:33