We have SharePoint Farms.  In order to get mail to them, we install smtp on them, then setup a corporate email address for their project.  That mailbox forwards call mail to a mail enabled contact with the servers name as part of the smtp address.  Something like..

Statistic@domain.com > Statistic@Server.domain.com

Then the sharepoint list picks it up.  We just migrated from Exchange 2007 to 2013 in the last 8 days.  After moving the mailboxes, one of them is sometimes duplication email.  That is..

Mail comes in to statistic.domain.com, that inbox only shows one email, when it's forwarded to the mail contact and then to the SharePoint server, it shows up as two email.

These emails almost always have attachments.  Sometimes two attachments.

I'm not sure when the email is showing up on the SharePoint server as two emails.

Thoughts?

Through troubleshooting I've found that this is only happening when email is sent from an eaternal source, but not when it's sent internally.

IE I send from yahoo.com i get two emails, i send from my AD domain.com address 1 copy.

I figured the problem out with the help of this thread..

https://social.technet.microsoft.com/Forums/exchange/en-US/97af4859-bdce-4041-aa22-36c618dd744c/duplicate-email-generated-when-forwarding?forum=exchangesvrsecuremessaginglegacy#f4496aa9-b362-4b21-9c24-842e1b683d50

Basically, in coexistence mode, saving a copy of the mail to the mailbox as well as forwarding it is causing it to be forwarded twice.  I unchecked save a copy to the mailbox, then tested and no more duplicates.

• Marked as answer by Amit TankMVP, Moderator 8 hours 3 minutes ago