Suddenly any email I send errors out with sender refused.
I verified the username and password and both Fetching mail and Sending mail pass verification.
Email sent anywhere even to the same domain fail.
I verified username and password with the providers webmail and they are correct.
I can send email from the web and Thunderbird without any issue.
I am receiving email but can not send any new emails.
Is the E-Mail address the correct address associated with your account? Some providers do not let you use aliases.
E.g., if your account is associated with login123@example.com, the provider might block any mail sent from john.doe@example.com or login123@example.arpa.
1 Like
Are you getting an error message from your smtp server, or is it a message when composing in K-9 Mail / Thunderbird? We had an issue that prevented sending in 11.0b1 that is fixed with 11.0b2
1 Like
The problem started Tuesday as I have sent messages on Monday.
It comes when I send the message and seems to be coming from the provider.
Would get a similar message if I was connected through a VPN but I know I am not
connected at this time.
P.S. I am on version 10
Can you separately install 11.0b2 and see if it is reproducible there as well? What is the exact message you are getting from your provider? Can you provide logs?
Optimum is blaming the app saying it is not supported that I must use Outlook.
All since Tuesday when it stopped working by Optimum refusing to accept email from K9mail.
I will try to load ver 11
The error message I get is Failed to send some messages. Sender refused
(Attachment k9mail-logs_(1)[1].txt is missing)
I tried to attach the log but it was rejected.
Installed Beta and it produced the same error message.
Could be SMTP: "HELO can't be [127.0.0.1]" · Issue #6327 · thunderbird/thunderbird-android · GitHub ? If you file an issue there you can also attach logs.
Are you in a corporate setting? If your administrator is limiting certain application IDs, you won’t be able to connect unless they add K-9/TV to the list if allowed MUAs.
I am not in a business setting but a home environment. Cablevision provides email to subscribers
the way Verizon used to before moving them to Yahoo mail.
I liked using Cablevisions mail since it as not scanned and the information sold like the “free” email
providers do.
This is unquestionably a provider (Optimum) issue.
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250-altprdrgo003.altice.prod.cloud.openwave.ai
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250-DSN
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250-8BITMIME
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250-AUTH=LOGIN
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250-AUTH LOGIN PLAIN
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250-DELIVERBY 300
05-16 13:41:42.115 21822 21841 V SmtpTransport: SMTP <<< 250 SIZE 104857600
05-16 13:41:42.115 21822 21841 D SmtpTransport: SMTP >>> sensitive
05-16 13:41:42.506 21822 21841 V SmtpTransport: SMTP <<< 235 [omitted]
05-16 13:41:42.507 21822 21841 D SmtpTransport: SMTP >>> MAIL FROM:pgenova@optonline.net BODY=8BITMIME
05-16 13:41:42.540 21822 21841 V SmtpTransport: SMTP <<< 550 Sender refused
05-16 13:41:42.541 21822 21841 D SmtpTransport: SMTP >>> QUIT
05-16 13:41:42.547 21822 21841 E MessagingController: Failed to send message
A valid username and domain yet it is refused.
Are you able to test this with another client that allows you to look at the logs at this level of detail to see if something is different? Does it actually work with Outlook via IMAP as they suggest?
Let me know if you don’t get through optonline support.
Yes I tested with Outlook on the phone and it works. I don’t see any place to debug outlook
to see what the difference is. On the phone Outlook sucks.
I sent several hours yesterday with Optimum on chat and then eventually on the phone.
Their answer was use Outlook period.
There might be a few other open source email clients that allow reviewing logs, maybe they have found a way. I’m curious if Outlook uses Exchange or IMAP with optonline, though not sure if that is possible to find out.
I did set it up with IMAP and I am actually responding now with Outlook.
I can confirm similar behavior that started this week (week of 5/12/25) with K9 and my Optimum account.
After over a year of using K9 with no issue, suddenly today I noticed that emails just stay stuck in the Outbox. Was able to successfully send an email from K9 as recently as this past Monday and absolutely nothing has changed on my end. Went to send an email this morning and after a few hours the recipient said he didn’t receive it. That’s when I noticed it sitting in the outbox. Receiving is fine.
Tried all the usual…delete app cache, uninstall, reboot phone, check outgoing server connection. Everything is fine, but email will not send.
Sending works fine with Outlook mobile as well as the GMail client. Very strange issue. Clearly Optimum changed something on their end that is now blocking K9.
1 Like
i’ m experiencing the same issue and time frame with optimum. They deny anything wrong on their side. Been using k9 mail for years. Mail works ok using their website app. Will continue to lodge support tickets to them.
1 Like
Confirming the issue is indeed It turns out the issue is SMTP: "HELO can't be [127.0.0.1]" · Issue #6327 · thunderbird/thunderbird-android · GitHub . They have restricted 127.0.0.1 as the EHLO IP address.
If you need an argument for support, the approach they are taking is not standards compliant. RFC 5321 specifically says:
An SMTP server MAY verify that the domain name argument in the EHLO
command actually corresponds to the IP address of the client.
However, if the verification fails, the server MUST NOT refuse to
accept a message on that basis. Information captured in the
verification attempt is for logging and tracing purposes.
So, it is a bug on their end.
1 Like