topic Re: eMail - mailbox cannot send (force9) in Email

eMail - mailbox cannot send (force9)

pottermus — Mon, 09 Jun 2025 10:41:13 GMT

i am a force9 user

I have a similar problem to other users in that recently my additional mailboxes have stopped being able to send from outlook (appears to be a username/password issue but these are correct and can login to use webmail)

main account works fine

main account + malbox name does not work (settings have not changed on multiple machines affected).

The issue exists connected to both the plusnet wifi and when connected to a different data usage device (phone) but I can send mail from webmail (both for main account and mailboxes)

I'm using POP3 but have tried configuring IMAP and this isn't working either (details provided appear to use the same outoing server relay.force9.net)

I've looked through mutliple posts but can't seem to find one where the issue is resolved. I have rebooted router but that hasn't helped (and doesn't feel like a robust solution).

I don't see how this can be anything at my side unless office has introduced something but again not sure that would explain why main account works and mailboxes don't

Any help would be much appreciated

Re: eMail - mailbox cannot send (force9)

dvorak — Mon, 09 Jun 2025 12:07:08 GMT

Moderators Note

This topic has been moved from Broadband to E-Mail

Re: eMail - mailbox cannot send (force9)

Townman — Mon, 09 Jun 2025 12:24:17 GMT

@pottermus

Hi a warm welcome to the forums.

Unfortunately issues which are NOT related to wrong credentials are reported as being a credentials issue. There is not such thing as "one resolution" as there are a multitude of potential issues. In the first instance, please use the email server connection diagnostics as described in the mail forum - see the link below.

Which version of "Outlook"? The 'proper' (paid for) version or the 'new' (free) version? You get what you pay for, the latter is a pig to configure, especially when all is going wrong. Switching between POP3 and IMAP is also asking for more complications as they nave nothing to do with sending. What is the exact error being reported?

Re: eMail - mailbox cannot send (force9)

pottermus — Mon, 09 Jun 2025 13:52:20 GMT

using curl on relay.force9.net for both the main account and the mailbox (account+mailbox) seems to have been successful - both appeared to connect.

We are using a paid for version of outlook and nothing has changed at our side for quite a long while and it's only in the past 2 months where the sending of mail became flaky and now 100% not possible.

the message from Send/Receive is

Task xxxxxx reorted an error (0x800CCC92) Your email server rejected your Login. Verify your username and password for this account in Account Settings

I have verified and they are correct (used in the curl command and i can login via webmail)

Re: eMail - mailbox cannot send (force9)

Townman — Mon, 09 Jun 2025 14:09:49 GMT

Given that

you can login via webmail (and send?)
the diagnostic curl commands login in OK
you are sure that the credentials are correct in outlook

... then though invalid credentials could be the cause, there are others too for this error code - a quick Google advises...

Error 0x800CCC92 in Outlook indicates a problem with your email account login, specifically that the email server is rejecting your login attempt. This usually means you have an issue with your username, password, or account settings.

Here's how to troubleshoot and fix the error:

1. Verify your credentials:

Double-check your username and password in Outlook's Account Settings. Make sure they are correct and match what your email provider uses.

2. Check your server settings:

Ensure that your incoming (POP) and outgoing (SMTP) server settings are correct. You can find this information on your email provider's website or by contacting their support.

3. Update your password:

If you've recently changed your password, update it in Outlook as well.

4. Create a new Outlook profile:

A corrupted profile can cause this error. Try creating a new profile and adding your account.

5. Log out of other devices:

Ensure that you are not logged in on other devices with the same account, as this can cause login conflicts.

6. Try Outlook's built-in repair feature:

Outlook has a built-in repair feature that can fix some account issues. You can find this in File > Account Settings > Account Settings.

7. Consider a PST file repair tool:

If the problem persists, a large or corrupted PST file can also cause this error. You might need to use a PST repair tool to fix it.

8. Check for add-ins:

Sometimes, add-ins can interfere with Outlook's functionality. Try starting Outlook in safe mode (Outlook /safe) to see if the issue is related to a specific add-in.

9. Contact Outlook.com support:

If you've tried these steps and the problem persists, contact Microsoft's Outlook.com support team for further assistance.

Personally I'd go for (8) first!

Re: eMail - mailbox cannot send (force9)

pottermus — Mon, 09 Jun 2025 14:44:53 GMT

I'll have a look at some of these things but it's happened on multiple machines for different mailboxes so can rule out anything related to the account other than all affected accounts are additional mailboxes to the main account. Nothing had been changed on any of the machines when it started happening and the server settings are correct (validated multiple times against what Plusnet support have provided and what is available in the User Guides).

My main issue here is that it was working on multiple machines (has been for many years), nothing has changed at my side and now it's not working - doesn't feel like the fix should be related to anything at my end.

Re: eMail - mailbox cannot send (force9)

Townman — Mon, 09 Jun 2025 17:56:03 GMT

This is reading rather odd!

If the cURL tests work and webmail works (can you please confirm you can send) then the issue points to the email clients.

Note that various posts around the place are no longer correct (or are incomplete) for server settings - please use those advised in the diagnostic script.

Force9 is very tidy, it will work with either email address or account+mailbox for secondary mailboxes. For clarity are you using an email address of you@youraccount.force9.co.uk or you@yourdomain.co.uk ?

Do double check that the server addresses are correct in the clients along with port numbers and encryption - some versions of Outlook set them back to its own guess every time you try to edit them. There is the possibility that Outlook has updated and got into a pickle. There's no harm in running the Microsoft365 repair option.

Re: eMail - mailbox cannot send (force9)

pottermus — Wed, 18 Jun 2025 07:25:50 GMT

So I've taken a blank laptop, installed MS Office (LTSC Professional Plus 2024) and tried to configure and it's still giving an error when using domain+mailbox@forece.net and not for domain@force9.net - this has always worked in the past and is how it's configured on other machines (which did wortk but now don't). After entering all the details., as per those provided by Plusnet, and that match previously working installs I am just presented with the popup asking me to put in accoutn details for relay.force9.net (and the credentials entered work ok as I can use them to login to webmail).

The machines that could previously send, but now can't are still able to receive mail.

I appreciate this doesn't sound right but machines that were working now aren't (without anything changing) and i can't do a new install - this doesn't feel like an issue at my side

Re: eMail - mailbox cannot send (force9)

Townman — Wed, 18 Jun 2025 08:48:17 GMT

Can you please run the email connection diagnostic- see link below. Use the settings it specifies for the client as unless there’s typos in the above post, they are not correct.

One matter that I am aware of is that if on the Plusnet network, bad credentials might be ignored as network level authentication is used instead. Also I think there’s some history of F9 credentials being forgiving if not specified correctly … force9 / F9 / account@domain. Most certainly the latter is not to specification.

Re: eMail - mailbox cannot send (force9)

Champnet — Wed, 18 Jun 2025 09:10:35 GMT

About a week ago my F9 email account on my iPad stopped working. It was continually trying to sync but as It has limited use I disabled it. After reading this post I re-enabled the account and all is working again. I did nothing my end so the problem is elsewhere…….

Re: eMail - mailbox cannot send (force9)

pottermus — Sun, 22 Jun 2025 13:29:03 GMT

The issue seems to have been resolved.

Previously (and worked for several years) the username was domain+mailbox@force9.net. I have now changed this to domain+mailbox and all machines/installs can now send and receive mail t their mailboxes.

For something so simple I would have expected Plusnet to be able to tell me this but putting that to one side it's now resolved

Thanks to all for your assistance

Re: eMail - mailbox cannot send (force9)

Townman — Sun, 22 Jun 2025 13:42:20 GMT

That might well have worked, but it is a malformed username. It should be one of...

account
account+secondarymailaddress
full email address

The demise of mal-formed usernames is a matter requiring attention on the migration pathway ... there are very few users using that format, so not exactly on the radar of CSC staff. Did you advise anyone that you were using this userID format when seeking help?

Re: eMail - mailbox cannot send (force9)

pottermus — Sun, 22 Jun 2025 13:53:03 GMT

So in your example you have used account+mailbox and i used the term domain+mailbox but as I have my own domain with Plusnet I beleive these are the same thing

And yes Plusnet was aware of the settings i was using as I shared a number of screenshots with them which included the original username

Re: eMail - mailbox cannot send (force9)

Townman — Sun, 22 Jun 2025 14:11:04 GMT

domain+mailbox I do not understand. The context of 'domain' here is ambiguous.

account.force9.co.uk is a domain derived from the account name
yourdomain.co.uk is also a domain which might be hosted on the account
fred@account.force9.co.uk and fred@yourdomain.co.uk are the same mailbox
assuming that this is not the DEFAULT mailbox, it can be accessed as
- account+fred
- fred@account.force9.co.uk
- fred@yourdomain.co.uk

Re: eMail - mailbox cannot send (force9)

pottermus — Sun, 22 Jun 2025 15:47:02 GMT

Well let's go with the fact that my username in the settings file, and using your language, is account+mailbox and this works so my issue is resolved.

Re: eMail - mailbox cannot send (force9)

MylesT — Mon, 14 Jul 2025 17:04:14 GMT

I have exactly the same problem and it also started on the 9th July. Did you manage to revolve this? Any help would be greatly appreciated

Re: eMail - mailbox cannot send (force9)

tjbuc — Mon, 14 Jul 2025 18:47:45 GMT

Hi MylesT

I also had this issue on 9th - 10th July (not sure exactly when it started as I was away from home most of last week) along with periodic POP3 and IMAP incoming mail access failures. Late on 10th July I spent some time trying to figure it out without any success (the email diagnostics didn't work for me). Then it started working again all by itself early afternoon on Friday 11th July and has been OK since (although I don't send many emails to notice when it may be down).

It's clear that the preparatory work for the migration to Greenby is having an impact on many users.

The only advice I can offer is to not change any of your settings and just wait.

Re: eMail - mailbox cannot send (force9)

Townman — Tue, 15 Jul 2025 08:51:03 GMT

@tjbuc / @MylesT

To be clear, this is an issue with Force9?

Are you connecting via the Plusnet network or are you connecting via a different ISP (off network)?

What user credentials are you using...

email address
accountname
accountname+mailbox

If the latter and off network, is it possibly a mail.bo address?

Can you please run the email server connectivity diagnostics - link below.

Re: eMail - mailbox cannot send (force9)

MylesT — Tue, 15 Jul 2025 09:08:33 GMT

My email address is with force9.

I am connecting through plusnet.

I am using accountname+mailbox.

Extract of the results from the email diagnostic are below

POP3

POP3 is fairly clear with its reason for the failure … however that is not the same as the cause of the failure:-

-ERR Login failed - check userID and password

I know the userID and password are correct as i can login to webmail.

Re: eMail - mailbox cannot send (force9)

Townman — Tue, 15 Jul 2025 09:28:19 GMT

OK - need to consider the possibility of this being a special character in the password issue...

Please try this format of the command...

curl.exe -v pop3s://mail.force9.net -u 'account+mailbox:password'

This negates the risk of there being a character in the password which might need to be escaped whey typed in. Please also report back the details which look like these...

* Host mail.force9.net:995 was resolved. * IPv6: (none) * IPv4: 91.204.208.196 * Trying 91.204.208.196:995...

That said, the detail you have reported is not what what I see on Win11 for a POP3 login failure...

< -ERR Login failed. * closing connection #0 curl: (67) Login denied

What is your environment / OS?