Question, we have a user who's calendar invites will be created and sent out, and then the same calendar invite will be sent out again a month later. Does anyone know how to fix this problem or what the solution is?

"Who's" means "who is".  I think you mean "whose".

Is this an Outlook user?  What version and service pack of Outlook?  Does this user have any other devices connecting to the mailbox, such as mobile devices, tablets, BlackBerries, Macs or the like?

Hi,

In addition, I want to double confirm this invite send out again in his Send folder or the invitee receive this meeting request again.
Just only one user facing this question? Please double check the outlook rule and add-in.

Please run Message Tracking log to get details about this message, also message header:
Get-MessageTrackingLog Server mailbox server Sender a@abc.com Recipient b@abc.com MessageSubject Read: message subject | Select Timestamp, ClientHostname,ServerHostname,Source,EventID,Recipients,RecipientStatus,Sender | ConvertTo-Html > C:\Test\Test.xml

Thanks

They are an Outlook user, but they are the only one who is having this issue. It is Outlook 2010 and I just started here but as far as I know, we update every patch Tuesday and whenever it is needed so I am guessing it has the latest service pack. I believe they do have an iPhone hooked up to the calendar and it is hooked up to our corporate calendar but they said they never use it to accept or send out meetings, or to send out emails in general.

Thank you for response