This topic

Can receive emails but not send - tricky description so please read text

matty1961 — Sat, 21 Mar 2026 22:34:44 GMT

Up until Friday, 13th March, we were using FTTC and copper to the house, and never had ANY issues with emails at all. Full Fibre was then installed on the Friday. All appeared well until opening Outlook Classic 365, when, after a few days of using Outlook, a pop-up window informed me I wasn't connected to the internet, when I plainly was.

Having formatted my machine, the issue disappeared, but another one has reared its ugly head.

I have 4 email accounts, with one being the default account. I can send and receive emails from the other 3 accounts. The default account receives emails but won't send them. It gets bounced back thus...

Title - System Administrator

Undeliverable Testing (Testing was the title of the email)

Your message did not reach some or all of the intended recipients.

Subject: testing

Sent: 21/03/2026 21:48

The following recipient(s) cannot be reached:

[email address] on 21/03/2026 21:48

This message could not be sent. You do not have the permission to send the message on behalf of the specified user.

It then gives me a whole page of error codes...

Diagnostic information for administrators:

__________________________________________________

Error is [0x80070005-0x000004dc-0x00000524].

Exchange response headers:

request-id: de9eb01f-7692-106c-6ca7-1592ff4719f1

X-ServerApplication: Exchange/15.20.9632.007

X-FEServer: LO4P123CA0467

X-CalculatedBETarget: AM0PR07MB5588.eurprd07.prod.outlook.com

X-RequestId: {08EB3534-287C-4AED-AE56-24F0C175338F}:51

X-ClientInfo: {9E2A6CE9-B57D-4C6D-8C3D-AF0B39424809}:239920042

X-ElapsedTime: 1022

X-BackEndHttpStatus: 200

X-ResponseCode: 0

X-RequestType: Execute

I have downloaded Thunderbird, and all my email accounts work. Using Outlook on the Web works, and New Outlook bundled with Windows 11 works (though I've been told that just accesses the web-based version.

Formatted my computer for the 4th time today, and I was able to send emails. I kept sending test emails. Snet on at 21:06, which was successful, but at 21:20 the email bounced back, unable to be sent.

Been onto Microsoft Support twice, the second time they want to escalate it to Level 2.

Btw, it is impossible to modify any server settings or port numbers in Outlook Classic 365 after you've added an email account.

Does anyone have any similar problems or can shed any light on this?

Many thanks.

Re: Can receive emails but not send - tricky description so please read text

licquorice — Sun, 22 Mar 2026 09:07:36 GMT

It is clearly an Outlook problem rather than BT. Outlook does seem to be problematic.

Are the other 3 accounts BTinternet accounts or other mail providers? If the latter, Outlook may be trying to send the BT mail via one of the other account's SMTP server which won't authenticate.

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sun, 22 Mar 2026 09:10:29 GMT

All 4 of the email accounts are outlook.com accounts.

Re: Can receive emails but not send - tricky description so please read text

licquorice — Sun, 22 Mar 2026 09:20:44 GMT

So why on earth are you posting on a BT forum?

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sun, 22 Mar 2026 09:27:46 GMT

Because BT Full Fibre is my broadband provider. It appeared to be working fine with ADSL, and I've only started having these issues since moving to Full Fibre. So the issue is either with BT or Outlook, or an incompatibility with both.

Why could I send an email perfectly at 9:06 pm, then at 9:20 pm, I sent the same test email to the same email address and got it bounced? I hadn't knowingly made ANY changes to my computer.

It doesn't make any sense. The ONLY thing that's changed is moving from ADSL to Full Fibre.

Re: Can receive emails but not send - tricky description so please read text

licquorice — Sun, 22 Mar 2026 09:31:57 GMT

But that's like blaming the electricity company for your television not working.

BT are just supplying a transparent pipe, there is absolutely no way they can affect just one account using a particular client.

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sun, 22 Mar 2026 09:39:15 GMT

On the face of it, I agree with you.

I have another ADSL connection with the same email addresses. I shall try that soon and get back to you.

I'm thinking it's something to do with the full fibre servers being configured differently from the ADSL servers.

Re: Can receive emails but not send - tricky description so please read text

licquorice — Sun, 22 Mar 2026 10:21:12 GMT

What servers? You are connecting to an Outlook server not a BT server.

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sun, 22 Mar 2026 12:11:07 GMT

Been on the BT website and raised a fault. Used the troubleshooter.

I removed the battery back-up, I've power cycled numerous times and changed he router for a new TP AX73 and every time I get this error...

Test results

You might have some connection stability issues. This can result in your connection dropping out.

Technical details
Your hub could be in sync with the exchange or cabinet, but not connecting to the gateway. If there's no PPP session it's likely to be a problem with our network.

SO it IS an issue with the fibre connection

Re: Can receive emails but not send - tricky description so please read text

licquorice — Sun, 22 Mar 2026 12:16:59 GMT

That is an entirely different thing.

How can BT differentiate between multiple Outlook email accounts and what client you use? Totally impossible.

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sun, 22 Mar 2026 12:18:35 GMT

Well... let's see what happens when this is resolved, because it's not helping.

Re: Can receive emails but not send - tricky description so please read text

licquorice — Sun, 22 Mar 2026 12:23:51 GMT

If you had no PPP session, nothing would work.

Re: Can receive emails but not send - tricky description so please read text

gg30340 — Sun, 22 Mar 2026 13:17:37 GMT

If all your Outlook.com email accounts work with Thunderbird and when using Webmail and only three out of the four work using the Outlook email client it would appear to be a problem with the set up of your Outlook email account in the Outlook email client, most likely a problem with the authentication of the errant email account on the outgoing Outlook servers.

I fail to see how it can in any way be down to moving from BT ADSL to FTTP. The delivery method of broadband is irrrelevant and if it in some strange unknow way was, why would it only select only one of your email accounts and not all of them and why would it not affect the accounts when using Thunderbird.

Try deleting the account from Outlook email client and restart your computer then set the account up again but this time set it up manually and enter all the settings using the correct settings supplied by Microsoft for the client.

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sat, 04 Apr 2026 08:04:54 GMT

Update... I finally managed to get an Openreach engineer round, and he checked as much as he could. Put a "meter" on the fibre optic and it measured -18.46 db. So everything appears to work normally, so it's not the cable.

My main computer was built by me, and I keep it updated. I also bouight a Geekom A5 mini-pc. Put a new NVMe drive in the A5 and installed the latest version of Windows 11. To cut a long story short. the A5 hasn't missed a beat. Sends emails through Outlook classic every time. My self-built computer still doesn't.

So I'm now thinking hardware?

Re: Can receive emails but not send - tricky description so please read text

gg30340 — Sat, 04 Apr 2026 08:10:45 GMT

@matty1961wrote:
So I'm now thinking hardware?

..... or how your account is set up in Outlook on your computer!

If it was hardware how does it only affect one email account of many and why only in Outlook.

Re: Can receive emails but not send - tricky description so please read text

matty1961 — Sat, 04 Apr 2026 08:14:17 GMT

I have absolutely no idea. The whole problem is crazy; it shouldn't happen like that. Never encountered anything this confusing. It doesn't make any sense at all.

Re: Can receive emails but not send - tricky description so please read text

gg30340 — Sat, 04 Apr 2026 11:29:11 GMT

@matty1961wrote:
I have absolutely no idea. The whole problem is crazy; it shouldn't happen like that. Never encountered anything this confusing. It doesn't make any sense at all.

It makes perfect sense if you pay attention to what has already been posted. The problem is with Outlook.

I will now bow out of your thread.

Re: Can receive emails but not send - Resolved!

matty1961 — Sun, 05 Apr 2026 08:56:21 GMT

You remember I posted about being unable to send emails from a specific account, well, I think I've resolved the issue.

Bought myself a USB wifi dongle. Disabled the onboard wifi and LAN, and plugged it in. To cut a long story short, sending and receiving emails, especially from the specific email account, has never missed a beat.

This morning I had further thoughts, and have been aware that the screw-in socket on my wifi antenna have been loose for a while.

I found some old wifi antennas and screwed them on. TA DAH!!!!!

Once again, it's never missed a beat (YET), and I'm getting a download speed of 540 Mbps on 5G wifi.

So it looks like it came down to a dodgy wifi antenna connection.

How very strange!

Re: Can receive emails but not send - Resolved!

gg30340 — Sun, 05 Apr 2026 13:34:42 GMT

If the problem has been resolved it is a coincidence that it happened when you tightened up your wifi aerial. There is no way that a faulty wifi aerial could differentiate between allowing all your Outlook email accounts to send emails except one.

It is more likely that your errant email account is now accessing a different Outlook server which is allowing the email through.

Any way glad you have it sorted.