How to fix "Operation cannot be performed because message has been changed" message. when using Outlook and Gmail.

Hi KeithLwood,

Thank you for the detail issue description.

May I first confirm with you if you are using Gmail account at outlook client or you are using Office365 account with its mailbox, it will be great if you tell us your account type. 

Since you have already did almost all the troubleshooting steps, regarding with the clean up boxes, can I ask if you did this as well?

Open Outlook > File > Options > Mail > Under Conversation Clean up, Uncheck When a reply modifies a message, don't move the original > Restart Outlook (it is is already unchecked, check it Restart Outlook, Uncheck it and Restart Outlook)

Also, try to Account Settings > Open your account > More settings > Under Advanced tab, put INBOX in Root Folder Path. (If your all folders disappear, simply remove INBOX from here)

Last, we would like you to create a new profile, navigate to control panel, Mail, and create a new one for your convience:

Let me know if the above steps work to some extent, apprecaite it.

Kind Regards,

George

Company has G Suite, so Google/Gmail hosts our email. I was using Office 2013 up until last week, now using Office 365. 

The conversation clean up check box you referenced was unchecked. I've tried that before. I've also tried creating a new profile. Same result. I have not tried moving my inbox to the Root Folder Path because I don't fully understand these instructions: (If your all folders disappear, simply remove INBOX from here)

PS, There is no >more settings under account settings. 

Options are: 

Hi KeithLwood,

In terms of the google account setting:

1. In Outlook 2016/2019, navigate to File > Account Settings > Account Settings.
2. Select the IMAP account and click Change (or double-click the IMAP account name)
3. Enter INBOX in the Root folder path field

You will see the window below:

Put INBOX in Root Folder Path, type the "INBOX".

Yours Sincerely,

George

This happens to me when I save and reopen an email out of drafts. I discovered a "work around": open the email to edit, delete the saved copy in drafts. Finish editing, hit send. 

I have the same issue with IMAP accounts (not GMail)

I too have tried the email cleanup fix, adding INBOX to the Root Folder path, deleting the user profile and account. Nothing seems to fix it.

The issue only occurs with Office 365/Outlook 2016 and not Outlook 2013.

Add me to the list of people with this problem in both Outlook 2016 and 2019 (on different machines), but it didn't happen with Outlook 2010 which I was using until earlier this year on the m/c that now has the 2019 version.

In my case I have a number of IMAP accounts including Gmail, and it appears to happen with any/all of them - sometimes "randomly"!

Therefore it looks to have been caused by the change in coding when Outlook 2016 was developed - and therefore Microsoft REALLY SHOULD take the responsibilty and FIX IT! :(.