Gmail download by Android/K-9 prevents pop3 download on linux/thunderbird

Hi everyone.
I work with K-9 v6.400 on Android 8.1 to download my email from my Google POP3 and other POP3 servers on my smartphone. I also use a Linux / Thunderbird 102.8 MUA to do the same from a desktop computer. But if I use one platform (smartphone or desktop) to download Gmail message, then those message become immediately unavailable for the other platform MUA, even though all downloaded messages are left on the Gmail POP3 server (and show there as read).

Note that POP3-downloading from an MTA different from Google works as I want it to. Downloading first on a platform email client does not prevent the second email client on the other platform to also be able to download the same email message.

I have checked my Android / K-9 and my Linux / Thunderbird 102.8 settings and there is nothing apparent there to cause this behavior. How can I download my Gmail messages on both platform’s MUAs successively ?

Also note that this used to work well for the Gmail POP3 MTA, with the same configuration of platforms and email apps (MUA). I also went to my Gmail account settings web page and have triple checked that the advised setting on the Thunderbird client is correct, i.e. to leave messages on Gmail POP3 server until I delete them", every time the said messages are downloaded by a POP3 client. No such setting exists on the Android / K-9 MUA.

Minor quibble: POP and IMAP servers are not MTAs.

Regardless, POP has never been the right protocol for mailboxes accessed from more than one MUA. Leave messages on server has always been a kludge at best. Other than force of habit, what is preventing you from using IMAP?

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Hi @linkp, thank you for your input.

“Important matters” first, in response to your “minor quibble”: K-9 or Thunderbird are MUAs that send their emails to an MTA via SMTP. The MTA ultimately transfers its payload to a mail delivery agent (MDA) which itself may use either Imap or Pop to distribute to another MUA interested in pulling the content of a certain email account… So yes, good point, MDAs are not MTAs are not MDAs. I was a bit quick on the vocabulary, even neglecting all the intervening network-middleware.

With POP I like the fact that I get to:

  • download my email and in so doing to free server (MDA) side resources (no indexing, no hogging resources when performing message searches, no maintaining a tCP connection open, …)
  • automatically rid the MDA of the Gigabytes of messages I have accumulated over the years,
  • manage my email locally with POP, nothing of my local eml tree shows on remote, meaning between other things, that it behooves me to make backups and all.

But mostly except for the fact that with POP I don’t actually need to send the content of an email twice to a server to first send it, second to hoard it there (that’s exactly what IMAP is happy to do for its users, I just don’t get why I can’t download my Goggle email from two POP3 mail clients (Android / K-9 and Linux / TB), when it’s possible with other private DMAs with the exact same configuration.

I guess I am just trying to understand what is going on … since when trying the same with the Android / original Gmail App, there is no issue; I can first visualize my email with the Gmail App on my smartphone (configured to pull messages using POP3) and then at any time later, I can download my email still using POP3 in my Linux / Thunderbird MUA.

Is there a trick here I’m missing with K-9 ? Or is it inherent to the interaction between K-9 and Google mail ? Can somebody give me pointers ?

POP3 should be used what it was designed for. Downloading messages and removing them from the server right afterwards. K-9 Mail doesn’t support this. So one should avoid using POP3 with K-9 Mail.

That being said, it sounds like you do want to keep messages on the server so another client can download and remove them afterwards. In that case, why not configure K-9 Mail to use IMAP? You can still use POP3 with the other client that actually keeps an archive of all your messages.

You can configure K-9 Mail to not upload sent messages. Although, I don’t think it makes a difference when using Gmail. I believe they will always store a copy of your message whenever you use their server to send it.

When using POP3, K-9 Mail will store sent messages in a local Sent folder. However, this is a dead end. K-9 Mail doesn’t support exporting messages. You will lose access to those messages when you lose access to the device. Even in benign cases like switching to a new device.

The last time I checked Gmail had four different ways POP3 can be configured. Chances are your Gmail account is configured to keep messages on the server and it will simply lie to your POP3 clients when they ask for a list of all messages on the server (because that list would be massive).

To summarize: don’t use POP3 with K-9 Mail. There’s a high chance you will regret this.


I use both K9 on phone and Thunderbird desktop. Both are IMAP to gmail.

I use Thunderbird to mass delete and for personal archiving. To do archiving, I select the messages to save and move those to a local Thunderbird folder (which K9 will never see). I could also copy messages in Thunderbird, making a second version.

I think Google lost a few messages of mine. I can query them, but can’t view them on the web or download them in Thunderbird.

And IMAP is fantastic!

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Gmail does not store messages “normal”. Tom Scott has a great video on the problems he ran into when trying to archive his mails from Gmail…

P.S.: Yes, the video only touches the mail problem as the initial hook, and the rest is about AI. But it still has an interesting insight into labelling of mails and intransparent messaging on Google’s side.

That’s exactly how I do it!

I have a bunch of storage folders in Thunderbird, seperated into stuff like Shops, (site) Registrations, Android, People etc.
Any email client on a PC has the advantage that you can select where to store your mails. I have those (and “My Documents”, Roaming folder and a few other other important ones) going to a seperate drive that gets backed up to yet another one every night at 3 AM. That way I can be sure not to lose (many of) them should my Windows drive die.

I used POP3 myself until a few years ago, but I’m happy that I took the plunge and switched to IMAP :slightly_smiling_face:

“POP3 should be used what it was designed for. Downloading messages and removing them from the server right afterwards. K-9 Mail doesn’t support this. So one should avoid using POP3 with K-9 Mail.”

The problem is, if one has been using K-9 (on a Chromebook in my case) for a long time with POP3, how can one convert to IMAP without losing what is stored in the Sent folder? I set up K-9 to use POP3 when I began using it, because that is what I knew. I knew nothing about IMAP other than the name. I have K-9/POP3 set to not delete message on the server unless I do so manually, because my email setup is kind of complicated, and I can access my mail in different ways on different devices.