Thunderbird IMAP failures when marking messages read or deleting them

Thunderbird IMAP failures when marking messages read or deleting them

In recent months, Thunderbird has been showing failures when marking messages read or deleting inbox messages in a Zoho IMAP account. At first, it happened sporadically, and now it occurs almost every time.
When I try to mark a message read, it reverts to unread a second or two later. If I keep doing so, it will eventually stay read after several attempts - sometimes 2-3, sometimes it takes up to 20, and today I couldn't mark a message read even after 50 attempts.
When I try to delete an incoming message, it reappears in the inbox - sometimes in a few seconds, sometimes much later. However, when I try to delete it again, Thunderbird sometimes (but not always) reports "UID move failed", and if I switch view to another folder and then go back to inbox, it may (or may not) be gone.
All this looks like an improperly handled race condition in IMAP. Notably, it happens in Thunderbird on Windows, but never in K-9 Mail on Android, so maybe it can be remedied by some Thunderbird settings, but which ones?
UPDATE: Now it happens in K-9, too :-( So the problem is definitely on Zoho's side.
    • Sticky Posts

    • Pocket from Mozilla is closing shop. Don’t lose your favorites . Move them to Zoho Mail Bookmarks now! 📥🔖

      The end of Pocket shouldn't mean the end of your important links and content. Easily import them into Zoho Mail's Bookmarks and continue right where you left off. You can bring over your entire Saves, Collections, and tags just the way they are. Bookmarks
    • Zoho Mail POP & IMAP Server Details

      Hello all! We have been receiving a number of requests regarding the errors while configuring or using Zoho Mail account in POP/ IMAP clients. The server details vary based on your account type and the Datacenter in which your account is setup. Ensure
    • Workplace - Zoholics Europe Customer Awards

      Dear Zoho Mail Community! 📣 We're excited to announce that at this year's Zoholics events across Europe, we're holding customer awards for the first time ever! Workplace - Zoholics Europe Customer Awards This is your chance to shout about the amazing
    • Important update on Group Management | Zoho Mail

      Dear Zoho Mail Community, This post is to inform you all of the following updates on the Group Management in Zoho Mail. Group Member Addition: If a group member is added to an organization group in a Zoho Application, the member will be automatically
    • Mastering email etiquette and best practices to follow in Zoho Mail

      Hello Zoho Mail Community, We’re thrilled to invite you all to our upcoming webinar: Mastering email etiquette and best practices to follow in Zoho Mail. Join our live webinar for expert etiquette tips to enhance your professionalism and elevate your