I've uncovered an issue with the POP mail service and Zoho.  I'm using Thunderbird as my mail client (I've been using it for nearly 15 years), and it suddenly stopped downloading email from Zoho.  I have a 30 GB allotment for my Zoho account, of which I was only using 12GB at the time it stopped downloading, so I should have plenty of overhead in terms of Zoho storage. 

At first I thought it was just a well known issue with Thunderbird, which is that Thunderbird has traditionally used the MBOX file format to store emails.  MBOX has a 4 GB limit, and over the years I've had to archive emails in my Thunderbird Inbox, reducing the inbox size (usually I'd archive an entire years of email, which opens plenty of overhead on the MBOX file limitation).  After doing that, emails would begin downloading again.  So that was what I tried first, and it seemed to work for a short period, but then I'd hit "Get Messages" in Thunderbird, and it would indicate "No knew messages on server."

However, there would be LOTS of new messages that it hadn't downloaded yet.  So I'd delete some local messages from Thunderbird, which would delete some messages from Zoho (I have my Thunderbird account set to delete messages from the server when I delete them locally), and that would allow mail to start flowing again.  So I thought the issue was still with my local Thunderbird instance, but I started to get suspicious of that, because I wasn't anywhere near the 4GB file limit for MBOX.  Even so, I decided to create an entirely new account in Thunderbird, using the newer file storage option (MAILDIR), which stores each email separately, instead of in a single file (hence eliminating the 4GB limit).

I created the new account, copied my emails from the old inbox in to the new inbox, and tried to get my new messages.  That's when I discovered that I now had to download over 50,000 emails.  Duplicates of what I've already downloaded, because a new POP account wants to grab EVERYTHING in the Inbox and Sent Messages folders.  There's an option to download only new messages, but that would mean i'd be missing older messages from the last few days, which Thunderbird hadn't yet downloaded.  So I decided to proceed and download ALL of my old messages again (I just created a filter to move the messages into a "duplicate emails folder" that I setup, and I'd just delete the old duplicate messages when it was done). 

So it seemed to be working, and then after 5 hours I hit another roadblock.  There's a 1GB daily download limit for Zoho, so I could no longer connect to the server to get mail.  After I discovered that problem, I used Zoho's "Unblock Me" tool to release the block (that's found here: https://mail.zoho.com/UnblockMe).  After that, I tried to resume downloading, and it worked for a bit, but then it was back to saying "no new messages on server" again, which is the original problem that got me to this point in the first place!  It had only downloaded my email up to August 12, 2018.  I was still missing everything after that.  I couldn't get Thunderbird to download any more emails. That's when I made a new discovery. 

I had gone into the Zoho mail interface to read my new email (I obviously can't do that in Thunderbird at this point, so I'm forced to use the Zoho interface), and I was deleting emails that I didn't need.  I have dual monitors, and on one screen I had Zoho open in a browser, and the other screen had Thunderbird open.  I have Thunderbird set to get new mail every minute.  Suddenly it downloaded 12 new messages (and by "new" I mean a few more old emails from August of 2018).  I realized I had just deleted about 15 messages in Zoho.  So then I decided to run a test, and delete some more messages in Zoho.  I went into my Sent Messages folder in Zoho (that's one of the two folders that POP3 downloads messages from, the other being the Inbox folder), and I deleted about 1000 old sent messages.  Suddenly Thunderbird started downloading email again.  It downloaded the rest of August 2018, and some of September 2018.  Progress!

I decided to delete all of my older Sent Messages in Zoho (Zoho has some nice options for emptying folders, where you can right click the folder, select "Empty Folder" and then set a date - it will delete anything older than the date you set).  So I deleted everything older than 2019 (basically, anything older than 12/31/2018).  That deleted well over 10,000 sent emails.  Suddenly my email started downloading in Thunderbird again!  Now I'm up to 4/8/2019.  Almost there, but email has stopped flowing again.  I need to delete thousands of more emails, in order to get caught up to 5/3/2019. 

That said, I shouldn't have to keep deleting email from Zoho, in order to be able to download email into Thunderbird!!!!  That's absurd.  The whole reason I paid for a 30GB account, is that I want to be able to leave at least two years worth of email on the mail server.  I have Thunderbird set to remove emails from Zoho, that are older than 720 days.  At the start of this process, when Thunderbird stopped being able to download emails (the problem first cropped up about 2 weeks ago), I had around 12 GB of email in Zoho.  Nowhere near my account limit of 30GB.  Now I have only have 7.6 GB of email, since I've deleted tons of older mail.  I can't understand why I need to keep deleting emails from Zoho, in order to be able to download messages into Thunderbird.  This makes no sense.  It never acted like this in the past two years that I've been using Zoho as my mail provider.

So my question is, has anyone else run into this problem?  I know most people use IMAP, and just leave everything on the server, but I prefer to archive all of my email locally, so I use POP3.  I can't continue using POP3 if it only lets me download email when I delete email from zoho!  Archiving mail in zoho doesn't help, because that doesn't actually remove it from a folder, it just doesn't display those messages that have been marked as archived.  It only allows me to download if I delete messages.  Delete 20 emails, download 18 emails (it's not equal - seems to be more related to the amount of data that each email accounts for - maybe 20 emails equals 500K of space, so it now downloads the equivalent of 500K of emails).  That's shouldn't be how this works. 

Also, this stopped working when I was at 12GB of email.  Now I'm at 7.6GB, and it's still not working.  It's like the trigger for downloading new mail is the fact that I've deleted mail in zoho (ie. free up space).  I can't just keep deleting mail in order for Thunderbird to be able to download emails.  That defeats the entire purpose of paying for a large amount of storage with Zoho! 

This only started in the last few weeks, so what changed Zoho????  Any suggestions?

Thanks,
- jeff