I have my OS X Mail client setup with one GMail and one Outlook account. They both use IMAP.

I have an issue that every time I reply to a message I send two identical replies (from the same hotmail address to the same recipient). This only happens when I reply with my hotmail address, writing a new message works as it is supposed to.

Mail version 8.0 (1990.1) and OS X 10.10.

I saw a previous poster had a similar issue but the problem solved itself in his/her case. Anyone got advice on how to fix this?


Edit: Here is the mail setup

  • Could you help us by showing/telling your settings in the email for the server to be used for hotmail under Mail Preferences Account. I have a smtp.live.com there for my hotmail. – Ruskes Nov 14 '14 at 17:21
  • Added to my post – Magnus Nov 15 '14 at 16:47
  • Thank you :) just to test, if you use the online outlook mail (not Apple Mail) and reply does it work. Reply to a sender from gmail or outlook? – Ruskes Nov 15 '14 at 17:02
  • It works fine with GMail, both web client and Mail. Outlook web client (and local Mac version) works fine as well. – Magnus Nov 15 '14 at 17:12
  • 1
    @Magnus did you solve the issue? – David Morales Jan 10 '15 at 21:53

This problem happens only for Hotmail accounts in MacOS Mail app. I also had this problem once. While to setting up hotmail account in mail app try to add it as Exchange account instead of using "Add another account". This process resolved my duplicate mails in sent folder issue for Hotmail account.

  • That completely solved the problem for me. I had the Hotmail account as IMAP, moved it to Exchange now. Everything works! – Anastasios Andronidis Nov 26 '19 at 17:22

You are most likely not sending each message twice, but saving two copies of it in your Sent folder.

Uncheck Store sent messages on the server under Mailbox Behaviors.

Your SMTP server automatically saves a copy of each outgoing message in your Sent folder. No need for Mail to duplicate that effort.

  • This is probably the correct answer. I noticed this with Gmail a while back. Google’s SMTP server automatically saves outgoing messages to your Sent folder. Having Mail do the same will result in duplicates. I bet this behavior applies to Hotmail. – user11633 Mar 29 '17 at 19:36

OK, the only settings i found that might cause that is in the Outlook web client.


Try setting it to as shown in pic above.

I assume the IMAP sync is doing something it should not.

But you can try resenting the outgoing server for outlook in Mail app.



Use this Apple tool to double check your email settings.

  • Sadly it did not work. I did also try tweaking the server settings and turning off saving sent messages on server as well. I will try to remove all mail accounts and add them again. – Magnus Nov 15 '14 at 18:35

Go to Mail -> Preferences -> Viewing and un-tick "Include related messages" in the View conversations section.


This is caused by usage of IMAP instead of Microsoft Exchange. It is a Microsoft email service after all.

Remove the account from the Mail application and add a new one via Mail -> Add account... -> Exchange.

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