In order to fix the "error occurred while moving messages to mailbox (null)" error you will need to assign severals in the Apple Mail client. The error often occurs when deleting messages while the Trash fodler has not been assigned in the Mac mail client. It can also occur when moving email between unassigned folders. The error appears in the client as follows:

Apple Mail error

In order to use these instructions, you will need to have added an email account into the Apple Mail client.

  1. Login to the Apple Mail Client
  2. choose folder to assign

    Scroll down to your newly added mail account. Click on the drop-arrow to see the Drafts, Sent, Junk, and Trash folders, then click on the Drafts folder to highlight it

  3.  Click on Use Mailbox as in menu

    In the Menu at the top of the screen, click on Mailbox, then scroll down to Use This Mailbox As

  4.  Click on Use Mailbox as in menu

    Click on "Drafts Mailbox" in the menu that appears to the right. This will assign the Drafts folder in the Apple mail client to the corresponding server folder.

  5. Repeat this action for your Sent, Junk, and Trash folders. Make sure to click on the respective folder assignment so that your files are going to the right place.

Congratulations! This fixes the "error occurred while moving messages to mailbox" error.

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n/a Points
2016-12-05 6:46 pm

Thank you! This problem has been haunting me for several months and I've searched many times on the Apple help pages and forum and not found anything referring to this. Your article was simple and concise and allowed me to fix everything in uder a minute.

Other search results stated that I was experiencing a flaw in the Mail App and there was nothing that could be done. Clearly there is, and you nailed it.

Tanks again

n/a Points
2017-04-04 4:07 pm

I do not have "Use This Mailbox As" option in the Sierra OS. What should I then do?

1,348 Points
2017-04-04 4:37 pm
It is possible that Apple has updated this procedure in the new versions of the program. I advise contacting Apple support for further assistance.
n/a Points
2018-04-14 10:01 am

The options are not highlighted after "use mailbox as" . How can I get them to highlight?

619 Points
2018-04-16 5:10 pm
If the options are grayed out then it's possible that they are already assigned. Are you receiving an error or experiencing an issue?
n/a Points
2018-10-13 8:21 am
Well written, thank you!
n/a Points
2019-04-17 6:41 pm
my mailbox does not have the dropdown you referred to.......
17,314 Points
2019-05-24 12:17 am
Hello Frank - the newer versions of Apple Mail handle this option differently. In the older versions of Mail, the Mailboxes can be designated to be used as Drafts Mailbox, Sent Mailbox, Trash Mailbox, and Archive Mailbox. In the latest version of Mail (in MacOS Mojave), They have a specific Junk folder and you can create mail boxes in it.
n/a Points
2019-08-29 2:47 pm

None of the above worked for me.. but what did work for my 5 emails was: 

1. Take each account offline - individually

right click on mailbox name, and "take offline"

*make sure you leave the one you think is a problem until last. 


then repeat the above but click "go online"... 


this could be a fluke, but everything is fine now and it's no longer trying to download 1 of 549 drafts (which I didn't have) or 1 of 21, 050 emails (which I didn't have either!)

n/a Points
2019-10-22 2:12 am

I don't have the option 'use the folder as'. It doesn't even show up under mailboxes. I am using os Mojave. Can you help?

17,314 Points
2019-10-22 10:54 pm
Hi Monica,

Apologies - this article is for an older version of Apple Mail. Check out this post for more assistance. We'll publish an updated article on this issue in the near future.

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