Emails stuck in outbox

Same kind of problem - mail stuck in outbox and won’t send. It’s only with ISP “” and its all fine with It started with K9 version 6.100 and continues with 6.200. A friend with a similar setup to mine had the same problem then K9 magically downgraded to 6.000 and it came right.

Question 1 - how do I get K9 to downgrade to 6.000
Question 2 - do you want more details to help debug the problem
Question 3 - how do I start a new topic on the forum instead of piggybacking on the previous discussion.

I can only answer question #1: Install the older version from here and set K-9 to not update in the Play Store settings.

Thanks Nimeuh. I tried downgrading to version 6.000 of K9 on an older phone but unfortunately it didn’t help.

Here is a restatement of the problem with more details.

The problem started about the time K9 was upgraded to 6.1000.

I cannot send mail when I use my ISP “”. The mail gets caught on the outbox.
But email works correctly if I use It also works correctly when I use Thunderbird on my desktop PC.

The error message with recent versions of K9 is

“Failed to send some messages
SmtpResponseParserException: Unexpected end of stream”

The relevant section of the error log is

07-21 17:01:38.311 8056 8376 I MessagingController: Running command ‘sendPendingMessages’, seq = 1175 (background priority)
07-21 17:01:38.335 8056 8376 I MessagingController: Scanning Outbox folder for messages to send
07-21 17:01:38.336 8056 8376 I MessagingController: Send count for message K9LOCAL:7d286420-743b-4837-ade2-160ea66ef232 is 0
07-21 17:01:38.358 8056 8376 V LockableDatabase: LockableDatabase: Transaction ended, took 13 ms / com.fsck.k9.mailstore.LocalMessage.setFlag(
07-21 17:01:38.359 8056 8376 I MessagingController: Sending message with UID K9LOCAL:7d286420-743b-4837-ade2-160ea66ef232
07-21 17:01:38.359 8056 8376 D SmtpTransport: SMTP >>> QUIT
07-21 17:01:41.699 8056 8376 V SmtpTransport: SMTP <<< 220 - ESMTP - alcott - Thu, 21 Jul 2022 17:01:43 +1200
07-21 17:01:41.700 8056 8376 D SmtpTransport: SMTP >>> EHLO []
07-21 17:01:41.739 8056 8376 V SmtpTransport: SMTP <<< 550-#h1 - An IP of as a HELO is not currently accepted due to high
07-21 17:01:41.739 8056 8376 V SmtpTransport: SMTP <<< 550 volumes of bot activity
07-21 17:01:41.740 8056 8376 V SmtpTransport: Server doesn’t support the EHLO command. Trying HELO…
07-21 17:01:41.741 8056 8376 D SmtpTransport: SMTP >>> HELO []
07-21 17:01:41.743 8056 8376 V SmtpTransport$logger: SMTP response data on parser error:
07-21 17:01:41.745 8056 8376 E MessagingController: Failed to send message
07-21 17:01:41.745 8056 8376 E MessagingController: com.fsck.k9.mail.transport.smtp.SmtpResponseParserException: Unexpected end of stream

My phone is a Nokia 9 running Android 10 and my K9 version 6.201.
I get the same behaviour on an HTC One_M8 running Android 6.
I have ESET Mobile Security on my Nokia but nothing like this on the HTC so I don’t think this is the problem.

A colleague with another model of Nokia running Android 10 and also using “” is experiencing a similar problem but it started a little later than with me and for a brief period the problem went away but has now reoccurred possibly when K9 upgraded to 6.201.

Any suggestions?

Your provider does not allow localhost as sender IP.

You have three options:

  1. Use a different app (Nine, R2Mail2, etc.pp.)
  2. Modify the K-9 source and compile your own fork
  3. Convince your provider to accept as sender IP

Similar problems related to localhost sender have been discussed throughout the forum.

Same problem here.

I temporarily had neither wifi nor mobile data while I sent a mail. After max_retries the mail was put in the outbox, but “send mails…” from the outbox menu does not work. So as a user you’re kind of stuck.

@cketti :
Couldn’t k9mail use a delay of say 2^n seconds and retry for n = 1,…,20?

And in particular reset the retry counter(s) (and permanentness of the error) when you tap “send mails…” in the outbox menu manually.


That would be a quiet long retry with several days on n=20. The idea is good but needs some value tweaking

I also like the idea to reset the retry counter.