I have seen one other person on this forum with the same issue. They concluded there was a bug in the godaddy software as it only affected IMAP on that specific site.

I have used IMAP on other domains in cPanel and Workspace but never encountered this before, been with GoDaddy for 15 years and used Thunderbird for several years now with no issues.

My best guess is a server issue from switching from cPanel to Workspace and it encountered a glitch in the matrix, but cannot figure out what.

I have installed Mailbird to test and do not get the problem there, not really wanting to install and delete many other clients but will if I need to confirm issue further. I figure since the problem did not happen on Mailbird then it most likely is a communication error with Thunderbird. I do not have this issue with this on my iPhone 6s Plus, only in Thunderbird.

I suggest you file a bug... https://bugzilla.mozilla.org/

If you are in a position to make an email account available to the developers so they can reproduce the issue your results will almost certainly be better.

I will file a bug report now and set up a test email account they can use. Thank you for the suggestion!

Nothing from Buzilla... The other strange thing that TB started today was also adding my reply in Drafts and not removing it after replying to the original email, this all on top of the original message still being marked as unread after reply.

I just installed eM Client for email and all is working fine there, may have to stop using TB which is sad as I love the UX in TB.

I have exactly the same problems using TB and IMAP at GoDaddy. Replied to emails are flagged as unread after a reply and drafts are accumulated and never deleted after sending an email. I need to manually delete them every time. I have had this problem for many months. I can't confirm if it started when I switched to IMAP because it was several years ago but I believe that I didn't have either problem until a long while after that switch. Showing an email as unread after a reply has been driving me crazy for a very long time.

I've been experiencing this same issue to using TB with Godaddy IMAP. It does appear that it's only been happening within maybe the last couple of months. Several of my coworkers have recently started complaining that their systems were behaving the same way.

I've noticed that the behavior happens at the moment when Thunderbird is "copying message to sent folder". When this message appears, the message goes from read status to unread (bolded).

For the record, I've been using Godaddy's IMAP service for 6 years, and have been a Thunderbird user longer than that. I'd really like to figure out the issue here.

Here's what all I've tested:

• DISABLE ALL ADDONS: Disabling all addons, and using default theme package. Same problem still exists.
• DISPLAY MESSAGE THREADS: Turning of "display message threads". Same problem still exists.
• LINUX TB: Testing from Linux desktop Thunderbird. Problem exists with Linux PC too.
• PREVIEW VS NEW WINDOW: Back to Windows, tested whether opening an email, then replying (rather than replying from Preview) has any effect. It didn't, same behavior. This is also true with TB in Linux.
• ADD-ON: In Thunderbird, installed Add-On, "Change quote and reply format" found here, https://nic-nac-project.org/~kaosmos/changequote-en.html. Once installed, you'll need to restart Thunderbird. From the addon settings, choose "Format and actions", and check the "Mark message as read after reply". This new add-on had no effect. I then sent myself a test email from Gmail and replied to it in Thunderbird. The message aster replying marked as unread. I uninstalled the add-on.
• QUICK FILTER: I'm now playing with Quick Filter up in the menu bar. This has no effect.
• CORRUPT FOLDER: Testing to see if TB folder is corrupt. I created new folder. I moved email into new folder, Test Folder. I then did a reply from new email, and it marked itself as unread after replying. By this, I'm thinking my Inbox is not corrupt.
• COMPACT: I have compacted the Inbox several times, but I'm still having same issue.
• TRY WITH DIFFERENT EMAIL VENDOR ACCOUNT (YAHOO & GMAIL): I added my Yahoo account to TB. I sent an email to my Yahoo account, and replied within Thunderbird. The message DID NOT mark itself unread. I also did the same thing adding my GMAIL account, and it behaved properly too. It did not mark the message unread after replying. The issue has to be with the Godaddy account.
• READ COLUMN: I removed the "Read" column (the one that shows green dot if red, and this had no effect.