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Unable to send blueyonder,co,uk emails on my iMac. iPad & iPhone are OK. Any suggestions?

Tuning in

For the last 48 hrs or so I have been unable to send emails from my iMac "using the server The server response was Authentication Required (VM401)" I have not altered mail settings in any way, and am still able to send emails using my iPhone and iPad. Anyone know what might be wrong ?


Forum Team
Forum Team

Hi Ed,

Thanks for posting, and sorry to see you're having some issues sending emails.

Just to confirm, is the problems sending via webmail or an email client?


I don't know. I'm not a computer expert. My iMac uses Apple's Mail version 16.0, outgoing mail account is, and host name is

Tuning in

My son has confirmed that it is an email client.


Hiya Ed, 

Thanks for coming back to us, sorry if you're still having this issue with your emails on your iMac!

Could you let us know the answers to these questions please - 

  • Is your iMac on the last software update?
  • Do you use a VPN?
  • Could you send us a screenshot of the error message you receive when you try to send an email?
  • Is it stopping emails going to ALL recipients, or just a select few? 



Tuning in

Thanks for your response. Answers to your questions are as follows:

My iMac is on the last software update - macOSVentura 13.6.7, I don't use a VPN, screenshot of error message attached, and it is stopping emails going to ALL recipients. Screenshot 2024-06-26 at 12.49.57.png



Tuning in

Unable to download error message, because it contains personal info. Taking out the personal info, it reads as follows -

Cannot send message using the server

The sender address was rejected by the server

The server response was: Authentication Required (VM401)

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent.

Sending from: Ed xxxxxx <>

Hello Ed,

Thanks for the extra information. 

What we need to do is take a look at this in a bit more depth.

The one thing you can try first is removing all your details from outlook logging out, then entering again as if you are starting over again.

The details you need are here 

Id that doesn't fix the issue please let us know.


I don’t use Outlook. I use Apple Mail version 16.0

Alessandro Volta

You need to use an app password with Apple Mail (explained below) and use the mail app settings as shown

VM seems to have tightened up some of its settings (for host name, port, authentication and app password) and any old/previous settings no longer work