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When I try to rename a mailbox, the name reverts to its former name after I type in the new one.
iMac (27-inch, Late 2013), macOS Sierra (10.12.3)
You can try this method in the article Rebuild mailboxes in Mail on Mac - Apple Support
But more effective way is delete the apple mail application from system preferences - internet account and once again configure with web account see this article Set up Mail on your Mac with email accounts - Apple Support
Third party applications , any anti virus , or softwares installed in Mac will only corrupt inbuilt apple application not even mail app other applications will also be effected and the system will start malfunctioning .
If there as such apps in your Mac please uninstall all of them use https://etrecheck.com/
And click on finder - click on applications you can manually read them and right click on unwanted applications only ( and do not try delete inbuilt apple app as they can't be deleted from Mac ) .
See this article macOS Sierra: Install, update, and uninstall apps
After that delete the mail application , all of the mails are stored on the servers they will start downloading again in apple mail application , as IMAP account has this feature .
A slight glitch as in your case of renaming mailboxes will sort out , but make sure delete all unwanted apps incase if they are used , any further questions / doubts please do ask .
Thank you for these suggestions. While either one would probably do the trick, they are more trouble than it's worth. I'll just keep the mailbox name as it is. I am mostly mystified by why there is a Rename option that doesn't work.
how to rename a mailbox
