When used as a Pop server, there appears to be only one way for a 3rd party mail client to delete mail from the Zoho server. That is:
- configure Zoho mail with the setting "Auto Delete Emails" - and -
- configure your Pop client to delete mail upon fetching it from the server.
However, I discovered that if a Pop client issues a delete request for mail, NOT when the mail was retrieved but at a later time, such mail is "flagged" as logically deleted by the Zoho server. Accordingly, if a Pop client on a second device (other than the one which issued the delete request) subsequently retrieves mail, all older mail flagged for deletion will not be retrieved.
Example:
I configure Thunderbird on my desktop computer to delete mail off the Zoho server after 1 day.
I allow Thunderbird to run every day, retrieving mail as usual and, I assume, issuing delete requests for mail older than 24 hours.
After several days, I run an email client on my Android device and retrieve new mail.
Only mail which is less than 24 hours old will be retrieved (mail that is NOT logically deleted / flagged).
However, in spite of this "logical" deletion which occurs with Pop clients, inspecting the Zoho mail inbox via the Zoho internet mail portal shows ALL mail on the server, both from the last 24 hours and older.
I've gotten these results using the android mail client K9, as well
as the stock android Gmail client (configured to access Zoho's pop
server).
So there appears to be some type of flag mechanism that is not visible via any email client app that can be set by an email client (Thunderbird in my case) and acknowledged by other email clients (K9, Gmail, etc.).
I wrote to Zoho about this, and in a response from Zoho support, they seemed to indicate that this logical deletion is how Pop servers are supposed to work. I agree, but I only question why other email hosts support a physical deletion for this function, but in Zoho's case it is only a "logical" flagging to let other Pop clients know that the mail shouldn't be retrieved. It used to work as a physical delete (circa 2019 and earlier?)
In my situation:
- I don't want my mail history in the "cloud" (Zoho server). I want to download it, archive it, and remove it from the server. My resource for doing this is my desktop computer running Thunderbird.
- I don't regularly use portable devices for handling email.
- The exception is if I'm on travel; Before I leave on my trip, I shut down Thunderbird on my desktop so it will no longer retrieve mail and clean up the server. I use my phone / tablet to continue to view mail while on the road. My portable devices leave all mail on the server.
- When I first turn on my portable device's email client, I'm not burdened with countless old mail messages which I've already processed; just the mail which arrived since the day before I shut down my desktop Thunderbird client.
- When I return from my trip, I launch Thunderbird and it retrieves and archives all mail that came in while I was on travel.
- Because I have configured Thunderbird to leave new mail on the server for 24 hours before deleting it, I can rely on "seeing" new mail on my phone as it arrives if I've only left the house for a few hours, even if I forget to shut down Thunderbird.
So just to summarize, the client email delete function didn't used to work this way, but since it does now, I'll have to remember to periodically sign on to Zoho mail via the internet portal and delete all my inbox mail.
I became aware of this because, along with myself, several users whom I support never access zoho mail via the internet portal. We only use email clients configured as I've described here. And so when this physical mail deletion stopped happening and mail boxes began to hit their 5GB limit, email accounts became temporarily suspended.