Emails shown in Sent, but not delivered to recipients

[tech_support_FKL]

For a while now, emails sent have been labelled as sent but not delivered to the respective recipients, Webmail seems to work okay, I am able to send and receive emails, Outlook is also able to receive emails,

The problem occurs when delivering mail, it does not seem to get to the recipient nor does a bounce-back message received.

Funny thing however is that outlook delivers response for replies to emails sent directly from webmail directly.

I have repaired outlook profile, removed and added back the same profile, ran Microsoft Support and Recovery Assistant, Uninstalled and reinstalled Office 365.

Given that the issue has affected around  9 devices as has been reported, it is not a single user issue.

If you have any ideas towards troubleshooting and discovering the root of the issue and how to solve it, kindly help out.

Thank you

[#2 · Accepted solution]

Hi,
I hope webmail works fine for all those affected devices and only Outlook app has this issue. Considering the above troubleshooting that you have already completed, can you check the Outlook add-ins, try to disable them based on their functionality and then send emails from those affected devices. Do let me know, how it goes...

[#3]

Outlook was working well, emails were being flagged as spam.