[IMAP] Unable to create folder "[user]@[hosted domain]/Sent/" on the server

[IMAP] Unable to create folder "[user]@[hosted domain]/Sent/" on the server

I have a domain hosted by Zoho and I am migrating away from Outlook as my email program.  I have been testing eM Client and Thunderbird.  With both email programs I run into a problem when I send email from my Zoho-hosted domain using eM Client or Thunderbird.  With eM Client I get an error message (image is attached):

[user]@[hosted domain]:An error occurred
[IMAP] Unable to create folder "[user]@[hosted domain]/Sent/" on the server. ([CANNOT] create failure: Folder: /Sent exists)

I thought that this was probably a problem with eM Client, but now I'm using Thunderbird and has a similar problem.  Thunderbird does not report an error but after pressing "Send" it says
Sending Message - [Subject]
Status: Copying message to Sent folder . . .
Progress: [Green Bar]

The process never completes  The only option at that point is to cancel sending the message.

I'm thinking something is wrong with the way Zoho is handling email sent by eM Client and Thunderbird using my Zoho-hosted account.  I didn't have a problem when I was using Outlook to send messages from my Zoho-hosted account.  But I would prefer not to have to start using Outlook again.

Thanks for any help you can provide.

Jim