Outlook very slow to send emails

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Outlook very slow to send emails

David Hair 0

MS Outlook is very slow sending BTinternet emails. I have tried both the classic and the new outlook, cleaned up everything , and even with 4KB of message it won't go. Sometimes if I log out and back in it works. This has been going on for months. Hotmail works almost instantly. Any advice would be appreciated.

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Answer 1

David Hair 0

Hi, I have tried all of your suggestions with no success.

Your first suggestion I have attached a screenshot showing the folder options, is this correct?

Your second suggestion is as per your set up

The third suggestion did not work.

BT webmail works almost instantly therefore you suggest it is the IMAP configuration. I have tried everything for the IMAP I can find on the internet but still no success.

Any further advice would be welcome. Regards [PII: Removed]

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Answer 2

Alice-N 8,415 Microsoft External Staff Moderator

Hi David Hair,

I hope you are doing well ! I just want to check if you have had a chance to test the steps earlier? Please let me know if they helped resolve the issue or if you are still experiencing any difficulties. I am here to assist you further.

Best Regards

David Hair 0 Reputation points

2026-03-31T12:35:21+00:00

Unfortunately despite following all your recommendations the problem persists. I have emails that simply won't send, others go ok. Ant further ideas?
Alice-N 8,415 Reputation points Microsoft External Staff Moderator

2026-04-02T04:58:22.3666667+00:00
Hi David Hair —I’m sorry it’s still happening. Since it’s intermittent (some send, some stall), please pinpoint where it’s getting stuck:

Is it stuck in Outbox? If yes, open the message > remove any attachment/signature image, save as Draft, then resend. Also try moving the stuck item from Outbox to Drafts and sending again.

Start Outlook in Safe Mode (rules/add-ins can delay SMTP):

Press Win + R > type: outlook.exe /safe Then test sending 2–3 short emails. If it works in Safe Mode, an add-in/rule may be the cause.

Try a different network (hotspot/mobile tether). If sending becomes instant, it points to ISP/router filtering or traffic shaping affecting BT’s SMTP route.

When it fails, please paste the exact Send/Receive error text (or screenshot) and confirm:

Does it stay in Outbox? or does it move to Sent Items but recipient doesn’t get it?

Thank you!
David Hair 0 Reputation points

2026-04-02T06:06:42.9+00:00

Hi, Thanks for your reply. I am using classic.

The emails are stuck in the outbox, if I save to draft they still remains in the outbox, see attachment at the bottom.

I have tried the safe mode, still the same. I have checked for add-in there are none and there are no rules.

I have tried hotspot via my phone, the internet works ok but still stuck in the outbox.

The emails stay in the outbox and don't move to sent. For some inexplicable reason the occasional email is sent.

Above are the IMAP settings.

Regards [PII: Removed]
Alice-N 8,415 Reputation points Microsoft External Staff Moderator

2026-04-03T01:01:50.69+00:00
Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi David Hair — thanks for confirming. Since Safe Mode + hotspot didn’t change anything and mail stays in Outbox, please try switching the SMTP send method (BT supports more than one) and forcing a full SMTP re-auth.

Change SMTP from 465 to 587

In the BT account “Outgoing mail” settings, change Port to 587 and set encryption to STARTTLS/TLS (keep SMTP authentication enabled). BT lists SMTP as 465 or 587 with SSL/TLS/TLS.

Force SMTP to use explicit credentials

Still in Outgoing settings, select “Log on using user name and password” (instead of “Use same settings as my incoming mail server”), then enter:

User name: your full BT email address

Password: your BT email password

This forces a clean SMTP auth handshake (sometimes “same as incoming” doesn’t re-prompt properly).

If it’s still intermittent: check for a BT-side sending restriction

Temporary send blocks can be triggered by things like recent password/security changes or sending to large recipient lists.

Please tell me how it goes. Have a lovely day!

Answer 3

Hi David Hair,

Thank you for reaching out to the Microsoft Q&A forum. I am happy to help you today. Based on your post, this is a consumer Outlook for Windows scenario using a third‑party IMAP account (BTinternet). Please try these (in order):

1, Check Outlook Send/Receive behavior (quick test)

In Classic Outlook:

Go to “Send / Receive”
Select “Send/Receive Groups” > “Define Send/Receive Groups”
Click “Edit” and make sure only “Inbox” is selected
Uncheck “Get folder unread count for subscribed folders”

2, Verify BT SMTP authentication settings

Please double‑check your BT account settings in Outlook match BT’s official requirements:

Outgoing server (SMTP): mail.btinternet.com
Port: 465
Encryption: SSL/TLS
“My outgoing server (SMTP) requires authentication” → Enabled

3, Test with a new Outlook profile

Corrupted profiles may cause long send delays with IMAP accounts.

Please follow:

Close Outlook
Open Control Panel > “Mail” > “Show Profiles”
Select “Add”, create a new profile
Add only the BTinternet account and test sending

As a final check:

Send the same email via BT Webmail
If it sends instantly there but not in Outlook, the issue is isolated to the local Outlook IMAP configuration

If the delay also happens in Webmail, you’ll need to contact BT support, as Outlook cannot control server‑side throttling or timeouts for third‑party providers.

Please tell me how it goes. If the problem persists, please don’t hesitate to reply to this thread and I will be happy to help. Have a lovely day!

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Outlook very slow to send emails

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