Mail client sending duplicate replies

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?

Regards

Edit: Here is the mail setup

Solution 1:

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.

Solution 2:

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.